array.rbs

# Arrays are ordered, integer-indexed collections of any object.
#
# Array indexing starts at 0, as in C or Java.  A negative index is assumed to
# be relative to the end of the array---that is, an index of -1 indicates the
# last element of the array, -2 is the next to last element in the array, and so
# on.
#
# ## Creating Arrays
#
# A new array can be created by using the literal constructor `[]`.  Arrays can
# contain different types of objects.  For example, the array below contains an
# Integer, a String and a Float:
#
#     ary = [1, "two", 3.0] #=> [1, "two", 3.0]
#
# An array can also be created by explicitly calling Array.new with zero, one
# (the initial size of the Array) or two arguments (the initial size and a
# default object).
#
#     ary = Array.new    #=> []
#     Array.new(3)       #=> [nil, nil, nil]
#     Array.new(3, true) #=> [true, true, true]
#
# Note that the second argument populates the array with references to the same
# object.  Therefore, it is only recommended in cases when you need to
# instantiate arrays with natively immutable objects such as Symbols, numbers,
# true or false.
#
# To create an array with separate objects a block can be passed instead. This
# method is safe to use with mutable objects such as hashes, strings or other
# arrays:
#
#     Array.new(4) {Hash.new}    #=> [{}, {}, {}, {}]
#     Array.new(4) {|i| i.to_s } #=> ["0", "1", "2", "3"]
#
# This is also a quick way to build up multi-dimensional arrays:
#
#     empty_table = Array.new(3) {Array.new(3)}
#     #=> [[nil, nil, nil], [nil, nil, nil], [nil, nil, nil]]
#
# An array can also be created by using the Array() method, provided by Kernel,
# which tries to call #to_ary, then #to_a on its argument.
#
#     Array({:a => "a", :b => "b"}) #=> [[:a, "a"], [:b, "b"]]
#
# ## Example Usage
#
# In addition to the methods it mixes in through the Enumerable module, the
# Array class has proprietary methods for accessing, searching and otherwise
# manipulating arrays.
#
# Some of the more common ones are illustrated below.
#
# ## Accessing Elements
#
# Elements in an array can be retrieved using the Array#[] method.  It can take
# a single integer argument (a numeric index), a pair of arguments (start and
# length) or a range. Negative indices start counting from the end, with -1
# being the last element.
#
#     arr = [1, 2, 3, 4, 5, 6]
#     arr[2]    #=> 3
#     arr[100]  #=> nil
#     arr[-3]   #=> 4
#     arr[2, 3] #=> [3, 4, 5]
#     arr[1..4] #=> [2, 3, 4, 5]
#     arr[1..-3] #=> [2, 3, 4]
#
# Another way to access a particular array element is by using the #at method
#
#     arr.at(0) #=> 1
#
# The #slice method works in an identical manner to Array#[].
#
# To raise an error for indices outside of the array bounds or else to provide a
# default value when that happens, you can use #fetch.
#
#     arr = ['a', 'b', 'c', 'd', 'e', 'f']
#     arr.fetch(100) #=> IndexError: index 100 outside of array bounds: -6...6
#     arr.fetch(100, "oops") #=> "oops"
#
# The special methods #first and #last will return the first and last elements
# of an array, respectively.
#
#     arr.first #=> 1
#     arr.last  #=> 6
#
# To return the first `n` elements of an array, use #take
#
#     arr.take(3) #=> [1, 2, 3]
#
# #drop does the opposite of #take, by returning the elements after `n` elements
# have been dropped:
#
#     arr.drop(3) #=> [4, 5, 6]
#
# ## Obtaining Information about an Array
#
# Arrays keep track of their own length at all times.  To query an array about
# the number of elements it contains, use #length, #count or #size.
#
#     browsers = ['Chrome', 'Firefox', 'Safari', 'Opera', 'IE']
#     browsers.length #=> 5
#     browsers.count #=> 5
#
# To check whether an array contains any elements at all
#
#     browsers.empty? #=> false
#
# To check whether a particular item is included in the array
#
#     browsers.include?('Konqueror') #=> false
#
# ## Adding Items to Arrays
#
# Items can be added to the end of an array by using either #push or #<<
#
#     arr = [1, 2, 3, 4]
#     arr.push(5) #=> [1, 2, 3, 4, 5]
#     arr << 6    #=> [1, 2, 3, 4, 5, 6]
#
# #unshift will add a new item to the beginning of an array.
#
#     arr.unshift(0) #=> [0, 1, 2, 3, 4, 5, 6]
#
# With #insert you can add a new element to an array at any position.
#
#     arr.insert(3, 'apple')  #=> [0, 1, 2, 'apple', 3, 4, 5, 6]
#
# Using the #insert method, you can also insert multiple values at once:
#
#     arr.insert(3, 'orange', 'pear', 'grapefruit')
#     #=> [0, 1, 2, "orange", "pear", "grapefruit", "apple", 3, 4, 5, 6]
#
# ## Removing Items from an Array
#
# The method #pop removes the last element in an array and returns it:
#
#     arr =  [1, 2, 3, 4, 5, 6]
#     arr.pop #=> 6
#     arr #=> [1, 2, 3, 4, 5]
#
# To retrieve and at the same time remove the first item, use #shift:
#
#     arr.shift #=> 1
#     arr #=> [2, 3, 4, 5]
#
# To delete an element at a particular index:
#
#     arr.delete_at(2) #=> 4
#     arr #=> [2, 3, 5]
#
# To delete a particular element anywhere in an array, use #delete:
#
#     arr = [1, 2, 2, 3]
#     arr.delete(2) #=> 2
#     arr #=> [1,3]
#
# A useful method if you need to remove `nil` values from an array is #compact:
#
#     arr = ['foo', 0, nil, 'bar', 7, 'baz', nil]
#     arr.compact  #=> ['foo', 0, 'bar', 7, 'baz']
#     arr          #=> ['foo', 0, nil, 'bar', 7, 'baz', nil]
#     arr.compact! #=> ['foo', 0, 'bar', 7, 'baz']
#     arr          #=> ['foo', 0, 'bar', 7, 'baz']
#
# Another common need is to remove duplicate elements from an array.
#
# It has the non-destructive #uniq, and destructive method #uniq!
#
#     arr = [2, 5, 6, 556, 6, 6, 8, 9, 0, 123, 556]
#     arr.uniq #=> [2, 5, 6, 556, 8, 9, 0, 123]
#
# ## Iterating over Arrays
#
# Like all classes that include the Enumerable module, Array has an each method,
# which defines what elements should be iterated over and how.  In case of
# Array's #each, all elements in the Array instance are yielded to the supplied
# block in sequence.
#
# Note that this operation leaves the array unchanged.
#
#     arr = [1, 2, 3, 4, 5]
#     arr.each {|a| print a -= 10, " "}
#     # prints: -9 -8 -7 -6 -5
#     #=> [1, 2, 3, 4, 5]
#
# Another sometimes useful iterator is #reverse_each which will iterate over the
# elements in the array in reverse order.
#
#     words = %w[first second third fourth fifth sixth]
#     str = ""
#     words.reverse_each {|word| str += "#{word} "}
#     p str #=> "sixth fifth fourth third second first "
#
# The #map method can be used to create a new array based on the original array,
# but with the values modified by the supplied block:
#
#     arr.map {|a| 2*a}     #=> [2, 4, 6, 8, 10]
#     arr                   #=> [1, 2, 3, 4, 5]
#     arr.map! {|a| a**2}   #=> [1, 4, 9, 16, 25]
#     arr                   #=> [1, 4, 9, 16, 25]
#
# ## Selecting Items from an Array
#
# Elements can be selected from an array according to criteria defined in a
# block.  The selection can happen in a destructive or a non-destructive manner.
#  While the destructive operations will modify the array they were called on,
# the non-destructive methods usually return a new array with the selected
# elements, but leave the original array unchanged.
#
# ### Non-destructive Selection
#
#     arr = [1, 2, 3, 4, 5, 6]
#     arr.select {|a| a > 3}       #=> [4, 5, 6]
#     arr.reject {|a| a < 3}       #=> [3, 4, 5, 6]
#     arr.drop_while {|a| a < 4}   #=> [4, 5, 6]
#     arr                          #=> [1, 2, 3, 4, 5, 6]
#
# ### Destructive Selection
#
# #select! and #reject! are the corresponding destructive methods to #select and
# #reject
#
# Similar to #select vs. #reject, #delete_if and #keep_if have the exact
# opposite result when supplied with the same block:
#
#     arr.delete_if {|a| a < 4}   #=> [4, 5, 6]
#     arr                         #=> [4, 5, 6]
#
#     arr = [1, 2, 3, 4, 5, 6]
#     arr.keep_if {|a| a < 4}   #=> [1, 2, 3]
#     arr                       #=> [1, 2, 3]
# for pack.c
#
class Array[unchecked out Elem] < Object
  include Enumerable[Elem, self]

  # Returns a new array.
  #
  # In the first form, if no arguments are sent, the new array will be empty. When
  # a `size` and an optional `default` are sent, an array is created with `size`
  # copies of `default`.  Take notice that all elements will reference the same
  # object `default`.
  #
  # The second form creates a copy of the array passed as a parameter (the array
  # is generated by calling to_ary on the parameter).
  #
  #     first_array = ["Matz", "Guido"]
  #
  #     second_array = Array.new(first_array) #=> ["Matz", "Guido"]
  #
  #     first_array.equal? second_array       #=> false
  #
  # In the last form, an array of the given size is created.  Each element in this
  # array is created by passing the element's index to the given block and storing
  # the return value.
  #
  #     Array.new(3) {|index| index ** 2}
  #     # => [0, 1, 4]
  #
  # ## Common gotchas
  #
  # When sending the second parameter, the same object will be used as the value
  # for all the array elements:
  #
  #     a = Array.new(2, Hash.new)
  #     # => [{}, {}]
  #
  #     a[0]['cat'] = 'feline'
  #     a # => [{"cat"=>"feline"}, {"cat"=>"feline"}]
  #
  #     a[1]['cat'] = 'Felix'
  #     a # => [{"cat"=>"Felix"}, {"cat"=>"Felix"}]
  #
  # Since all the Array elements store the same hash, changes to one of them will
  # affect them all.
  #
  # If multiple copies are what you want, you should use the block version which
  # uses the result of that block each time an element of the array needs to be
  # initialized:
  #
  #     a = Array.new(2) {Hash.new}
  #     a[0]['cat'] = 'feline'
  #     a # => [{"cat"=>"feline"}, {}]
  #
  def initialize: () -> void
                | (::Array[Elem] ary) -> void
                | (int size, ?Elem val) -> void
                | (int size) { (::Integer index) -> Elem } -> void

  # Returns a new array populated with the given objects.
  #
  #     Array.[]( 1, 'a', /^A/)  # => [1, "a", /^A/]
  #     Array[ 1, 'a', /^A/ ]    # => [1, "a", /^A/]
  #     [ 1, 'a', /^A/ ]         # => [1, "a", /^A/]
  #
  def self.[]: [U] (*U) -> ::Array[U]

  # Tries to convert `obj` into an array, using the `to_ary` method.  Returns the
  # converted array or `nil` if `obj` cannot be converted. This method can be used
  # to check if an argument is an array.
  #
  #     Array.try_convert([1])   #=> [1]
  #     Array.try_convert("1")   #=> nil
  #
  #     if tmp = Array.try_convert(arg)
  #       # the argument is an array
  #     elsif tmp = String.try_convert(arg)
  #       # the argument is a string
  #     end
  #
  def self.try_convert: [U] (untyped) -> ::Array[U]?

  public

  # Set Intersection --- Returns a new array containing unique elements common to
  # the two arrays. The order is preserved from the original array.
  #
  # It compares elements using their #hash and #eql? methods for efficiency.
  #
  #     [ 1, 1, 3, 5 ] & [ 3, 2, 1 ]                 #=> [ 1, 3 ]
  #     [ 'a', 'b', 'b', 'z' ] & [ 'a', 'b', 'c' ]   #=> [ 'a', 'b' ]
  #
  # See also Array#uniq.
  #
  def &: (::Array[untyped] | _ToAry[untyped]) -> ::Array[Elem]

  # Repetition --- With a String argument, equivalent to `ary.join(str)`.
  #
  # Otherwise, returns a new array built by concatenating the `int` copies of
  # `self`.
  #
  #     [ 1, 2, 3 ] * 3    #=> [ 1, 2, 3, 1, 2, 3, 1, 2, 3 ]
  #     [ 1, 2, 3 ] * ","  #=> "1,2,3"
  #
  def *: (string str) -> ::String
       | (int int) -> ::Array[Elem]

  # Concatenation --- Returns a new array built by concatenating the two arrays
  # together to produce a third array.
  #
  #     [ 1, 2, 3 ] + [ 4, 5 ]    #=> [ 1, 2, 3, 4, 5 ]
  #     a = [ "a", "b", "c" ]
  #     c = a + [ "d", "e", "f" ]
  #     c                         #=> [ "a", "b", "c", "d", "e", "f" ]
  #     a                         #=> [ "a", "b", "c" ]
  #
  # Note that
  #     x += y
  #
  # is the same as
  #     x = x + y
  #
  # This means that it produces a new array. As a consequence, repeated use of
  # `+=` on arrays can be quite inefficient.
  #
  # See also Array#concat.
  #
  def +: [U] (_ToAry[U]) -> ::Array[Elem | U]

  # Array Difference
  #
  # Returns a new array that is a copy of the original array, removing all
  # occurrences of any item that also appear in `other_ary`. The order is
  # preserved from the original array.
  #
  # It compares elements using their #hash and #eql? methods for efficiency.
  #
  #     [ 1, 1, 2, 2, 3, 3, 4, 5 ] - [ 1, 2, 4 ]  #=>  [ 3, 3, 5 ]
  #
  # Note that while 1 and 2 were only present once in the array argument, and were
  # present twice in the receiver array, all occurrences of each Integer are
  # removed in the returned array.
  #
  # If you need set-like behavior, see the library class Set.
  #
  # See also Array#difference.
  #
  def -: (_ToAry[untyped]) -> ::Array[Elem]

  # Append---Pushes the given object on to the end of this array. This expression
  # returns the array itself, so several appends may be chained together.
  #
  #     a = [ 1, 2 ]
  #     a << "c" << "d" << [ 3, 4 ]
  #             #=>  [ 1, 2, "c", "d", [ 3, 4 ] ]
  #     a
  #             #=>  [ 1, 2, "c", "d", [ 3, 4 ] ]
  #
  def <<: (Elem) -> self

  # Comparison --- Returns an integer (`-1`, `0`, or `+1`) if this array is less
  # than, equal to, or greater than `other_ary`.
  #
  # Each object in each array is compared (using the <=> operator).
  #
  # Arrays are compared in an "element-wise" manner; the first element of `ary` is
  # compared with the first one of `other_ary` using the <=> operator, then each
  # of the second elements, etc... As soon as the result of any such comparison is
  # non zero (i.e. the two corresponding elements are not equal), that result is
  # returned for the whole array comparison.
  #
  # If all the elements are equal, then the result is based on a comparison of the
  # array lengths. Thus, two arrays are "equal" according to Array#<=> if, and
  # only if, they have the same length and the value of each element is equal to
  # the value of the corresponding element in the other array.
  #
  # `nil` is returned if the `other_ary` is not an array or if the comparison of
  # two elements returned `nil`.
  #
  #     [ "a", "a", "c" ]    <=> [ "a", "b", "c" ]   #=> -1
  #     [ 1, 2, 3, 4, 5, 6 ] <=> [ 1, 2 ]            #=> +1
  #     [ 1, 2 ]             <=> [ 1, :two ]         #=> nil
  #
  def <=>: (untyped) -> ::Integer?

  # Equality --- Two arrays are equal if they contain the same number of elements
  # and if each element is equal to (according to Object#==) the corresponding
  # element in `other_ary`.
  #
  #     [ "a", "c" ]    == [ "a", "c", 7 ]     #=> false
  #     [ "a", "c", 7 ] == [ "a", "c", 7 ]     #=> true
  #     [ "a", "c", 7 ] == [ "a", "d", "f" ]   #=> false
  #
  def ==: (untyped other) -> bool

  # Element Reference --- Returns the element at `index`, or returns a subarray
  # starting at the `start` index and continuing for `length` elements, or returns
  # a subarray specified by `range` of indices.
  #
  # Negative indices count backward from the end of the array (-1 is the last
  # element).  For `start` and `range` cases the starting index is just before an
  # element.  Additionally, an empty array is returned when the starting index for
  # an element range is at the end of the array.
  #
  # Returns `nil` if the index (or starting index) are out of range.
  #
  #     a = [ "a", "b", "c", "d", "e" ]
  #     a[2] +  a[0] + a[1]    #=> "cab"
  #     a[6]                   #=> nil
  #     a[1, 2]                #=> [ "b", "c" ]
  #     a[1..3]                #=> [ "b", "c", "d" ]
  #     a[4..7]                #=> [ "e" ]
  #     a[6..10]               #=> nil
  #     a[-3, 3]               #=> [ "c", "d", "e" ]
  #     # special cases
  #     a[5]                   #=> nil
  #     a[6, 1]                #=> nil
  #     a[5, 1]                #=> []
  #     a[5..10]               #=> []
  #
  def []: (int index) -> Elem
        | (int start, int length) -> ::Array[Elem]?
        | (::Range[::Integer] range) -> ::Array[Elem]?

  # Element Assignment --- Sets the element at `index`, or replaces a subarray
  # from the `start` index for `length` elements, or replaces a subarray specified
  # by the `range` of indices.
  #
  # If indices are greater than the current capacity of the array, the array grows
  # automatically.  Elements are inserted into the array at `start` if `length` is
  # zero.
  #
  # Negative indices will count backward from the end of the array.  For `start`
  # and `range` cases the starting index is just before an element.
  #
  # An IndexError is raised if a negative index points past the beginning of the
  # array.
  #
  # See also Array#push, and Array#unshift.
  #
  #     a = Array.new
  #     a[4] = "4";                 #=> [nil, nil, nil, nil, "4"]
  #     a[0, 3] = [ 'a', 'b', 'c' ] #=> ["a", "b", "c", nil, "4"]
  #     a[1..2] = [ 1, 2 ]          #=> ["a", 1, 2, nil, "4"]
  #     a[0, 2] = "?"               #=> ["?", 2, nil, "4"]
  #     a[0..2] = "A"               #=> ["A", "4"]
  #     a[-1]   = "Z"               #=> ["A", "Z"]
  #     a[1..-1] = nil              #=> ["A", nil]
  #     a[1..-1] = []               #=> ["A"]
  #     a[0, 0] = [ 1, 2 ]          #=> [1, 2, "A"]
  #     a[3, 0] = "B"               #=> [1, 2, "A", "B"]
  #
  def []=: (int index, Elem obj) -> Elem
         | (int start, int length, Elem obj) -> Elem
         | (int start, int length, ::Array[Elem]) -> ::Array[Elem]
         | (int start, int length, nil) -> nil
         | (::Range[::Integer], Elem obj) -> Elem
         | (::Range[::Integer], ::Array[Elem]) -> ::Array[Elem]
         | (::Range[::Integer], nil) -> nil

  # See also Enumerable#all?
  #
  def all?: () -> bool
          | (_Pattern[Elem] pattern) -> bool
          | () { (Elem obj) -> boolish } -> bool

  # See also Enumerable#any?
  #
  alias any? all?

  alias append push

  # Searches through an array whose elements are also arrays comparing `obj` with
  # the first element of each contained array using `obj.==`.
  #
  # Returns the first contained array that matches (that is, the first associated
  # array), or `nil` if no match is found.
  #
  # See also Array#rassoc
  #
  #     s1 = [ "colors", "red", "blue", "green" ]
  #     s2 = [ "letters", "a", "b", "c" ]
  #     s3 = "foo"
  #     a  = [ s1, s2, s3 ]
  #     a.assoc("letters")  #=> [ "letters", "a", "b", "c" ]
  #     a.assoc("foo")      #=> nil
  #
  def assoc: (untyped) -> ::Array[untyped]?

  # Returns the element at `index`. A negative index counts from the end of
  # `self`. Returns `nil` if the index is out of range. See also Array#[].
  #
  #     a = [ "a", "b", "c", "d", "e" ]
  #     a.at(0)     #=> "a"
  #     a.at(-1)    #=> "e"
  #
  def at: (int index) -> Elem?

  # By using binary search, finds a value from this array which meets the given
  # condition in O(log n) where n is the size of the array.
  #
  # You can use this method in two modes: a find-minimum mode and a find-any mode.
  #  In either case, the elements of the array must be monotone (or sorted) with
  # respect to the block.
  #
  # In find-minimum mode (this is a good choice for typical use cases), the block
  # must always return true or false, and there must be an index i (0 <= i <=
  # ary.size) so that:
  #
  # *   the block returns false for any element whose index is less than i, and
  # *   the block returns true for any element whose index is greater than or
  #     equal to i.
  #
  #
  # This method returns the i-th element.  If i is equal to ary.size, it returns
  # nil.
  #
  #     ary = [0, 4, 7, 10, 12]
  #     ary.bsearch {|x| x >=   4 } #=> 4
  #     ary.bsearch {|x| x >=   6 } #=> 7
  #     ary.bsearch {|x| x >=  -1 } #=> 0
  #     ary.bsearch {|x| x >= 100 } #=> nil
  #
  # In find-any mode (this behaves like libc's bsearch(3)), the block must always
  # return a number, and there must be two indices i and j (0 <= i <= j <=
  # ary.size) so that:
  #
  # *   the block returns a positive number for [ary](k) if 0 <= k < i,
  # *   the block returns zero for [ary](k) if i <= k < j, and
  # *   the block returns a negative number for [ary](k) if j <= k < ary.size.
  #
  #
  # Under this condition, this method returns any element whose index is within
  # i...j.  If i is equal to j (i.e., there is no element that satisfies the
  # block), this method returns nil.
  #
  #     ary = [0, 4, 7, 10, 12]
  #     # try to find v such that 4 <= v < 8
  #     ary.bsearch {|x| 1 - x / 4 } #=> 4 or 7
  #     # try to find v such that 8 <= v < 10
  #     ary.bsearch {|x| 4 - x / 2 } #=> nil
  #
  # You must not mix the two modes at a time; the block must always return either
  # true/false, or always return a number.  It is undefined which value is
  # actually picked up at each iteration.
  #
  def bsearch: () { (Elem) -> (true | false) } -> Elem?
             | () { (Elem) -> ::Integer } -> Elem?

  # By using binary search, finds an index of a value from this array which meets
  # the given condition in O(log n) where n is the size of the array.
  #
  # It supports two modes, depending on the nature of the block. They are exactly
  # the same as in the case of the #bsearch method, with the only difference being
  # that this method returns the index of the element instead of the element
  # itself. For more details consult the documentation for #bsearch.
  #
  def bsearch_index: () { (Elem) -> (true | false) } -> ::Integer?
                   | () { (Elem) -> ::Integer } -> ::Integer?

  # Removes all elements from `self`.
  #
  #     a = [ "a", "b", "c", "d", "e" ]
  #     a.clear    #=> [ ]
  #
  def clear: () -> self

  # Invokes the given block once for each element of `self`.
  #
  # Creates a new array containing the values returned by the block.
  #
  # See also Enumerable#collect.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  #     a = [ "a", "b", "c", "d" ]
  #     a.collect {|x| x + "!"}           #=> ["a!", "b!", "c!", "d!"]
  #     a.map.with_index {|x, i| x * i}   #=> ["", "b", "cc", "ddd"]
  #     a                                 #=> ["a", "b", "c", "d"]
  #
  def collect: [U] () { (Elem item) -> U } -> ::Array[U]
             | () -> ::Enumerator[Elem, ::Array[untyped]]

  # Invokes the given block once for each element of `self`, replacing the element
  # with the value returned by the block.
  #
  # See also Enumerable#collect.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  #     a = [ "a", "b", "c", "d" ]
  #     a.map! {|x| x + "!" }
  #     a #=>  [ "a!", "b!", "c!", "d!" ]
  #     a.collect!.with_index {|x, i| x[0...i] }
  #     a #=>  ["", "b", "c!", "d!"]
  #
  # collect! is monomorphic because of RBS limitation.
  def collect!: () { (Elem item) -> Elem } -> self
              | () -> ::Enumerator[Elem, self]

  # When invoked with a block, yields all combinations of length `n` of elements
  # from the array and then returns the array itself.
  #
  # The implementation makes no guarantees about the order in which the
  # combinations are yielded.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  # Examples:
  #
  #     a = [1, 2, 3, 4]
  #     a.combination(1).to_a  #=> [[1],[2],[3],[4]]
  #     a.combination(2).to_a  #=> [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]
  #     a.combination(3).to_a  #=> [[1,2,3],[1,2,4],[1,3,4],[2,3,4]]
  #     a.combination(4).to_a  #=> [[1,2,3,4]]
  #     a.combination(0).to_a  #=> [[]] # one combination of length 0
  #     a.combination(5).to_a  #=> []   # no combinations of length 5
  #
  def combination: (int n) { (::Array[Elem]) -> void } -> self
                 | (int n) -> ::Enumerator[::Array[Elem], self]

  # Returns a copy of `self` with all `nil` elements removed.
  #
  #     [ "a", nil, "b", nil, "c", nil ].compact
  #                       #=> [ "a", "b", "c" ]
  #
  def compact: () -> ::Array[Elem]

  # Removes `nil` elements from the array.
  #
  # Returns `nil` if no changes were made, otherwise returns the array.
  #
  #     [ "a", nil, "b", nil, "c" ].compact! #=> [ "a", "b", "c" ]
  #     [ "a", "b", "c" ].compact!           #=> nil
  #
  def compact!: () -> self?

  # Appends the elements of `other_ary`s to `self`.
  #
  #     [ "a", "b" ].concat( ["c", "d"])   #=> [ "a", "b", "c", "d" ]
  #     [ "a" ].concat( ["b"], ["c", "d"]) #=> [ "a", "b", "c", "d" ]
  #     [ "a" ].concat #=> [ "a" ]
  #
  #     a = [ 1, 2, 3 ]
  #     a.concat( [ 4, 5 ])
  #     a                                 #=> [ 1, 2, 3, 4, 5 ]
  #
  #     a = [ 1, 2 ]
  #     a.concat(a, a)                    #=> [1, 2, 1, 2, 1, 2]
  #
  # See also Array#+.
  #
  def concat: (*::Array[Elem] arrays) -> ::Array[Elem]

  # Returns the number of elements.
  #
  # If an argument is given, counts the number of elements which equal `obj` using
  # `==`.
  #
  # If a block is given, counts the number of elements for which the block returns
  # a true value.
  #
  #     ary = [1, 2, 4, 2]
  #     ary.count                  #=> 4
  #     ary.count(2)               #=> 2
  #     ary.count {|x| x%2 == 0}   #=> 3
  #
  def count: () -> ::Integer
           | (untyped obj) -> ::Integer
           | () { (Elem) -> boolish } -> ::Integer

  # Calls the given block for each element `n` times or forever if `nil` is given.
  #
  # Does nothing if a non-positive number is given or the array is empty.
  #
  # Returns `nil` if the loop has finished without getting interrupted.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  #     a = ["a", "b", "c"]
  #     a.cycle {|x| puts x}       # print, a, b, c, a, b, c,.. forever.
  #     a.cycle(2) {|x| puts x}    # print, a, b, c, a, b, c.
  #
  def cycle: (?int? n) { (Elem) -> void } -> nil
           | (?int? n) -> ::Enumerator[Elem, nil]

  def deconstruct: () -> self

  # Deletes all items from `self` that are equal to `obj`.
  #
  # Returns the last deleted item, or `nil` if no matching item is found.
  #
  # If the optional code block is given, the result of the block is returned if
  # the item is not found.  (To remove `nil` elements and get an informative
  # return value, use Array#compact!)
  #
  #     a = [ "a", "b", "b", "b", "c" ]
  #     a.delete("b")                   #=> "b"
  #     a                               #=> ["a", "c"]
  #     a.delete("z")                   #=> nil
  #     a.delete("z") {"not found"}     #=> "not found"
  #
  def delete: (untyped obj) -> Elem?
            | [S, T] (S obj) { (S) -> T } -> (Elem | T)

  # Deletes the element at the specified `index`, returning that element, or `nil`
  # if the `index` is out of range.
  #
  # See also Array#slice!
  #
  #     a = ["ant", "bat", "cat", "dog"]
  #     a.delete_at(2)    #=> "cat"
  #     a                 #=> ["ant", "bat", "dog"]
  #     a.delete_at(99)   #=> nil
  #
  def delete_at: (int index) -> Elem?

  # Deletes every element of `self` for which block evaluates to `true`.
  #
  # The array is changed instantly every time the block is called, not after the
  # iteration is over.
  #
  # See also Array#reject!
  #
  # If no block is given, an Enumerator is returned instead.
  #
  #     scores = [ 97, 42, 75 ]
  #     scores.delete_if {|score| score < 80 }   #=> [97]
  #
  def delete_if: () { (Elem item) -> boolish } -> self
               | () -> ::Enumerator[Elem, self]

  # Array Difference
  #
  # Returns a new array that is a copy of the original array, removing all
  # occurrences of any item that also appear in `other_ary`. The order is
  # preserved from the original array.
  #
  # It compares elements using their #hash and #eql? methods for efficiency.
  #
  #     [ 1, 1, 2, 2, 3, 3, 4, 5 ].difference([ 1, 2, 4 ])     #=> [ 3, 3, 5 ]
  #
  # Note that while 1 and 2 were only present once in the array argument, and were
  # present twice in the receiver array, all occurrences of each Integer are
  # removed in the returned array.
  #
  # Multiple array arguments can be supplied and all occurrences of any element in
  # those supplied arrays that match the receiver will be removed from the
  # returned array.
  #
  #     [ 1, 'c', :s, 'yep' ].difference([ 1 ], [ 'a', 'c' ])  #=> [ :s, "yep" ]
  #
  # If you need set-like behavior, see the library class Set.
  #
  # See also Array#-.
  #
  def difference: (*::Array[untyped] arrays) -> ::Array[Elem]

  # Extracts the nested value specified by the sequence of *idx* objects by
  # calling `dig` at each step, returning `nil` if any intermediate step is `nil`.
  #
  #     a = [[1, [2, 3]]]
  #
  #     a.dig(0, 1, 1)                    #=> 3
  #     a.dig(1, 2, 3)                    #=> nil
  #     a.dig(0, 0, 0)                    #=> TypeError: Integer does not have #dig method
  #     [42, {foo: :bar}].dig(1, :foo)    #=> :bar
  #
  def dig: (int idx) -> Elem?
         | (int idx, untyped, *untyped) -> untyped

  # Drops first `n` elements from `ary` and returns the rest of the elements in an
  # array.
  #
  # If a negative number is given, raises an ArgumentError.
  #
  # See also Array#take
  #
  #     a = [1, 2, 3, 4, 5, 0]
  #     a.drop(3)             #=> [4, 5, 0]
  #
  def drop: (int n) -> ::Array[Elem]

  # Drops elements up to, but not including, the first element for which the block
  # returns `nil` or `false` and returns an array containing the remaining
  # elements.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  # See also Array#take_while
  #
  #     a = [1, 2, 3, 4, 5, 0]
  #     a.drop_while {|i| i < 3 }   #=> [3, 4, 5, 0]
  #
  def drop_while: () { (Elem obj) -> boolish } -> ::Array[Elem]
                | () -> ::Enumerator[Elem, ::Array[Elem]]

  # Calls the given block once for each element in `self`, passing that element as
  # a parameter.  Returns the array itself.
  #
  # If no block is given, an Enumerator is returned.
  #
  #     a = [ "a", "b", "c" ]
  #     a.each {|x| print x, " -- " }
  #
  # produces:
  #
  #     a -- b -- c --
  #
  def each: () -> ::Enumerator[Elem, self]
          | () { (Elem item) -> void } -> self

  # Same as Array#each, but passes the `index` of the element instead of the
  # element itself.
  #
  # An Enumerator is returned if no block is given.
  #
  #     a = [ "a", "b", "c" ]
  #     a.each_index {|x| print x, " -- " }
  #
  # produces:
  #
  #     0 -- 1 -- 2 --
  #
  def each_index: () { (::Integer index) -> void } -> self
                | () -> ::Enumerator[Elem, self]

  # Returns `true` if `self` contains no elements.
  #
  #     [].empty?   #=> true
  #
  def empty?: () -> bool

  # Returns `true` if `self` and `other` are the same object, or are both arrays
  # with the same content (according to Object#eql?).
  #
  def eql?: (untyped other) -> bool

  # Tries to return the element at position `index`, but throws an IndexError
  # exception if the referenced `index` lies outside of the array bounds.  This
  # error can be prevented by supplying a second argument, which will act as a
  # `default` value.
  #
  # Alternatively, if a block is given it will only be executed when an invalid
  # `index` is referenced.
  #
  # Negative values of `index` count from the end of the array.
  #
  #     a = [ 11, 22, 33, 44 ]
  #     a.fetch(1)               #=> 22
  #     a.fetch(-1)              #=> 44
  #     a.fetch(4, 'cat')        #=> "cat"
  #     a.fetch(100) {|i| puts "#{i} is out of bounds"}
  #                              #=> "100 is out of bounds"
  #
  def fetch: (int index) -> Elem
           | [T] (int index, T default) -> (Elem | T)
           | [T] (int index) { (int index) -> T } -> (Elem | T)

  # The first three forms set the selected elements of `self` (which may be the
  # entire array) to `obj`.
  #
  # A `start` of `nil` is equivalent to zero.
  #
  # A `length` of `nil` is equivalent to the length of the array.
  #
  # The last three forms fill the array with the value of the given block, which
  # is passed the absolute index of each element to be filled.
  #
  # Negative values of `start` count from the end of the array, where `-1` is the
  # last element.
  #
  #     a = [ "a", "b", "c", "d" ]
  #     a.fill("x")              #=> ["x", "x", "x", "x"]
  #     a.fill("z", 2, 2)        #=> ["x", "x", "z", "z"]
  #     a.fill("y", 0..1)        #=> ["y", "y", "z", "z"]
  #     a.fill {|i| i*i}         #=> [0, 1, 4, 9]
  #     a.fill(-2) {|i| i*i*i}   #=> [0, 1, 8, 27]
  #
  def fill: (Elem obj) -> self
          | (Elem obj, int? start, ?int? length) -> self
          | (Elem obj, ::Range[::Integer] range) -> self
          | (?int? start, ?int? length) { (::Integer index) -> Elem } -> self
          | (::Range[::Integer] range) { (::Integer index) -> Elem } -> self

  # Returns a new array containing all elements of `ary` for which the given
  # `block` returns a true value.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  #     [1,2,3,4,5].select {|num| num.even? }     #=> [2, 4]
  #
  #     a = %w[ a b c d e f ]
  #     a.select {|v| v =~ /[aeiou]/ }    #=> ["a", "e"]
  #
  # See also Enumerable#select.
  #
  # Array#filter is an alias for Array#select.
  #
  def filter: () { (Elem item) -> boolish } -> ::Array[Elem]
            | () -> ::Enumerator[Elem, ::Array[Elem]]

  # Invokes the given block passing in successive elements from `self`, deleting
  # elements for which the block returns a `false` value.
  #
  # The array may not be changed instantly every time the block is called.
  #
  # If changes were made, it will return `self`, otherwise it returns `nil`.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  # See also Array#keep_if.
  #
  # Array#filter! is an alias for Array#select!.
  #
  def filter!: () { (Elem item) -> boolish } -> self?
             | () -> ::Enumerator[Elem, self?]

  # Returns the *index* of the first object in `ary` such that the object is `==`
  # to `obj`.
  #
  # If a block is given instead of an argument, returns the *index* of the first
  # object for which the block returns `true`.  Returns `nil` if no match is
  # found.
  #
  # See also Array#rindex.
  #
  # An Enumerator is returned if neither a block nor argument is given.
  #
  #     a = [ "a", "b", "c" ]
  #     a.index("b")              #=> 1
  #     a.index("z")              #=> nil
  #     a.index {|x| x == "b"}    #=> 1
  #
  def find_index: (untyped obj) -> ::Integer?
                | () { (Elem item) -> boolish } -> ::Integer?
                | () -> ::Enumerator[Elem, ::Integer?]

  # Returns the first element, or the first `n` elements, of the array. If the
  # array is empty, the first form returns `nil`, and the second form returns an
  # empty array. See also Array#last for the opposite effect.
  #
  #     a = [ "q", "r", "s", "t" ]
  #     a.first     #=> "q"
  #     a.first(2)  #=> ["q", "r"]
  #
  def first: () -> Elem?
           | (int n) -> ::Array[Elem]

  # Returns a new array that is a one-dimensional flattening of `self`
  # (recursively).
  #
  # That is, for every element that is an array, extract its elements into the new
  # array.
  #
  # The optional `level` argument determines the level of recursion to flatten.
  #
  #     s = [ 1, 2, 3 ]           #=> [1, 2, 3]
  #     t = [ 4, 5, 6, [7, 8] ]   #=> [4, 5, 6, [7, 8]]
  #     a = [ s, t, 9, 10 ]       #=> [[1, 2, 3], [4, 5, 6, [7, 8]], 9, 10]
  #     a.flatten                 #=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  #     a = [ 1, 2, [3, [4, 5] ] ]
  #     a.flatten(1)              #=> [1, 2, 3, [4, 5]]
  #
  def flatten: (?int level) -> ::Array[untyped]

  # Flattens `self` in place.
  #
  # Returns `nil` if no modifications were made (i.e., the array contains no
  # subarrays.)
  #
  # The optional `level` argument determines the level of recursion to flatten.
  #
  #     a = [ 1, 2, [3, [4, 5] ] ]
  #     a.flatten!   #=> [1, 2, 3, 4, 5]
  #     a.flatten!   #=> nil
  #     a            #=> [1, 2, 3, 4, 5]
  #     a = [ 1, 2, [3, [4, 5] ] ]
  #     a.flatten!(1) #=> [1, 2, 3, [4, 5]]
  #
  def flatten!: (?int level) -> self?

  # Compute a hash-code for this array.
  #
  # Two arrays with the same content will have the same hash code (and will
  # compare using #eql?).
  #
  # See also Object#hash.
  #
  def hash: () -> ::Integer

  # Returns `true` if the given `object` is present in `self` (that is, if any
  # element `==` `object`), otherwise returns `false`.
  #
  #     a = [ "a", "b", "c" ]
  #     a.include?("b")   #=> true
  #     a.include?("z")   #=> false
  #
  def include?: (untyped object) -> bool

  # Returns the *index* of the first object in `ary` such that the object is `==`
  # to `obj`.
  #
  # If a block is given instead of an argument, returns the *index* of the first
  # object for which the block returns `true`.  Returns `nil` if no match is
  # found.
  #
  # See also Array#rindex.
  #
  # An Enumerator is returned if neither a block nor argument is given.
  #
  #     a = [ "a", "b", "c" ]
  #     a.index("b")              #=> 1
  #     a.index("z")              #=> nil
  #     a.index {|x| x == "b"}    #=> 1
  #
  alias index find_index

  # Inserts the given values before the element with the given `index`.
  #
  # Negative indices count backwards from the end of the array, where `-1` is the
  # last element. If a negative index is used, the given values will be inserted
  # after that element, so using an index of `-1` will insert the values at the
  # end of the array.
  #
  #     a = %w{ a b c d }
  #     a.insert(2, 99)         #=> ["a", "b", 99, "c", "d"]
  #     a.insert(-2, 1, 2, 3)   #=> ["a", "b", 99, "c", 1, 2, 3, "d"]
  #
  def insert: (int index, *Elem obj) -> self

  # Creates a string representation of `self`, by calling #inspect on each
  # element.
  #
  #     [ "a", "b", "c" ].to_s     #=> "[\"a\", \"b\", \"c\"]"
  #
  def inspect: () -> String

  # Set Intersection --- Returns a new array containing unique elements common to
  # `self` and `other_ary`s. Order is preserved from the original array.
  #
  # It compares elements using their #hash and #eql? methods for efficiency.
  #
  #     [ 1, 1, 3, 5 ].intersection([ 3, 2, 1 ])                    # => [ 1, 3 ]
  #     [ "a", "b", "z" ].intersection([ "a", "b", "c" ], [ "b" ])  # => [ "b" ]
  #     [ "a" ].intersection #=> [ "a" ]
  #
  # See also Array#&.
  #
  def intersection: (*::Array[untyped] | _ToAry[untyped] other_ary) -> ::Array[Elem]

  # Returns a string created by converting each element of the array to a string,
  # separated by the given `separator`. If the `separator` is `nil`, it uses
  # current `$,`. If both the `separator` and `$,` are `nil`, it uses an empty
  # string.
  #
  #     [ "a", "b", "c" ].join        #=> "abc"
  #     [ "a", "b", "c" ].join("-")   #=> "a-b-c"
  #
  # For nested arrays, join is applied recursively:
  #
  #     [ "a", [1, 2, [:x, :y]], "b" ].join("-")   #=> "a-1-2-x-y-b"
  #
  def join: (?string separator) -> String

  # Deletes every element of `self` for which the given block evaluates to
  # `false`, and returns `self`.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  #     a = %w[ a b c d e f ]
  #     a.keep_if {|v| v =~ /[aeiou]/ }    #=> ["a", "e"]
  #     a                                  #=> ["a", "e"]
  #
  # See also Array#select!.
  #
  def keep_if: () { (Elem item) -> boolish } -> self
             | () -> ::Enumerator[Elem, self]

  # Returns the last element(s) of `self`. If the array is empty, the first form
  # returns `nil`.
  #
  # See also Array#first for the opposite effect.
  #
  #     a = [ "w", "x", "y", "z" ]
  #     a.last     #=> "z"
  #     a.last(2)  #=> ["y", "z"]
  #
  def last: () -> Elem?
          | (int n) -> ::Array[Elem]

  # Returns the number of elements in `self`. May be zero.
  #
  #     [ 1, 2, 3, 4, 5 ].length   #=> 5
  #     [].length                  #=> 0
  #
  def length: () -> ::Integer

  # Invokes the given block once for each element of `self`.
  #
  # Creates a new array containing the values returned by the block.
  #
  # See also Enumerable#collect.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  #     a = [ "a", "b", "c", "d" ]
  #     a.collect {|x| x + "!"}           #=> ["a!", "b!", "c!", "d!"]
  #     a.map.with_index {|x, i| x * i}   #=> ["", "b", "cc", "ddd"]
  #     a                                 #=> ["a", "b", "c", "d"]
  #
  alias map collect

  # Invokes the given block once for each element of `self`, replacing the element
  # with the value returned by the block.
  #
  # See also Enumerable#collect.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  #     a = [ "a", "b", "c", "d" ]
  #     a.map! {|x| x + "!" }
  #     a #=>  [ "a!", "b!", "c!", "d!" ]
  #     a.collect!.with_index {|x, i| x[0...i] }
  #     a #=>  ["", "b", "c!", "d!"]
  #
  alias map! collect!

  # Returns the object in *ary* with the maximum value. The first form assumes all
  # objects implement Comparable; the second uses the block to return *a <=> b*.
  #
  #     ary = %w(albatross dog horse)
  #     ary.max                                   #=> "horse"
  #     ary.max {|a, b| a.length <=> b.length}    #=> "albatross"
  #
  # If the `n` argument is given, maximum `n` elements are returned as an array.
  #
  #     ary = %w[albatross dog horse]
  #     ary.max(2)                                  #=> ["horse", "dog"]
  #     ary.max(2) {|a, b| a.length <=> b.length }  #=> ["albatross", "horse"]
  #
  def max: () -> Elem?
         | () { (Elem a, Elem b) -> ::Integer? } -> Elem?
         | (int n) -> ::Array[Elem]
         | (int n) { (Elem a, Elem b) -> ::Integer? } -> ::Array[Elem]

  # Returns the object in *ary* with the minimum value. The first form assumes all
  # objects implement Comparable; the second uses the block to return *a <=> b*.
  #
  #     ary = %w(albatross dog horse)
  #     ary.min                                   #=> "albatross"
  #     ary.min {|a, b| a.length <=> b.length}    #=> "dog"
  #
  # If the `n` argument is given, minimum `n` elements are returned as an array.
  #
  #     ary = %w[albatross dog horse]
  #     ary.min(2)                                  #=> ["albatross", "dog"]
  #     ary.min(2) {|a, b| a.length <=> b.length }  #=> ["dog", "horse"]
  #
  alias min max

  # Returns a two element array which contains the minimum and the maximum value
  # in the array.
  #
  # Can be given an optional block to override the default comparison method `a
  # <=> b`.
  #
  def minmax: () -> [ Elem?, Elem? ]
            | () { (Elem a, Elem b) -> ::Integer? } -> [ Elem?, Elem? ]

  # See also Enumerable#none?
  #
  alias none? all?

  # See also Enumerable#one?
  #
  alias one? none?

  # Packs the contents of *arr* into a binary sequence according to the directives
  # in *aTemplateString* (see the table below) Directives ``A,'' ``a,'' and ``Z''
  # may be followed by a count, which gives the width of the resulting field. The
  # remaining directives also may take a count, indicating the number of array
  # elements to convert. If the count is an asterisk (```*`''), all remaining
  # array elements will be converted. Any of the directives ```sSiIlL`'' may be
  # followed by an underscore (```_`'') or exclamation mark (```!`'') to use the
  # underlying platform's native size for the specified type; otherwise, they use
  # a platform-independent size. Spaces are ignored in the template string. See
  # also String#unpack.
  #
  #     a = [ "a", "b", "c" ]
  #     n = [ 65, 66, 67 ]
  #     a.pack("A3A3A3")   #=> "a  b  c  "
  #     a.pack("a3a3a3")   #=> "a\000\000b\000\000c\000\000"
  #     n.pack("ccc")      #=> "ABC"
  #
  # If *aBufferString* is specified and its capacity is enough, `pack` uses it as
  # the buffer and returns it. When the offset is specified by the beginning of
  # *aTemplateString*, the result is filled after the offset. If original contents
  # of *aBufferString* exists and it's longer than the offset, the rest of
  # *offsetOfBuffer* are overwritten by the result. If it's shorter, the gap is
  # filled with ```\0`''.
  #
  # Note that ``buffer:'' option does not guarantee not to allocate memory in
  # `pack`.  If the capacity of *aBufferString* is not enough, `pack` allocates
  # memory.
  #
  # Directives for `pack`.
  #
  #     Integer       | Array   |
  #     Directive     | Element | Meaning
  #     ----------------------------------------------------------------------------
  #     C             | Integer | 8-bit unsigned (unsigned char)
  #     S             | Integer | 16-bit unsigned, native endian (uint16_t)
  #     L             | Integer | 32-bit unsigned, native endian (uint32_t)
  #     Q             | Integer | 64-bit unsigned, native endian (uint64_t)
  #     J             | Integer | pointer width unsigned, native endian (uintptr_t)
  #                   |         | (J is available since Ruby 2.3.)
  #                   |         |
  #     c             | Integer | 8-bit signed (signed char)
  #     s             | Integer | 16-bit signed, native endian (int16_t)
  #     l             | Integer | 32-bit signed, native endian (int32_t)
  #     q             | Integer | 64-bit signed, native endian (int64_t)
  #     j             | Integer | pointer width signed, native endian (intptr_t)
  #                   |         | (j is available since Ruby 2.3.)
  #                   |         |
  #     S_ S!         | Integer | unsigned short, native endian
  #     I I_ I!       | Integer | unsigned int, native endian
  #     L_ L!         | Integer | unsigned long, native endian
  #     Q_ Q!         | Integer | unsigned long long, native endian (ArgumentError
  #                   |         | if the platform has no long long type.)
  #                   |         | (Q_ and Q! is available since Ruby 2.1.)
  #     J!            | Integer | uintptr_t, native endian (same with J)
  #                   |         | (J! is available since Ruby 2.3.)
  #                   |         |
  #     s_ s!         | Integer | signed short, native endian
  #     i i_ i!       | Integer | signed int, native endian
  #     l_ l!         | Integer | signed long, native endian
  #     q_ q!         | Integer | signed long long, native endian (ArgumentError
  #                   |         | if the platform has no long long type.)
  #                   |         | (q_ and q! is available since Ruby 2.1.)
  #     j!            | Integer | intptr_t, native endian (same with j)
  #                   |         | (j! is available since Ruby 2.3.)
  #                   |         |
  #     S> s> S!> s!> | Integer | same as the directives without ">" except
  #     L> l> L!> l!> |         | big endian
  #     I!> i!>       |         | (available since Ruby 1.9.3)
  #     Q> q> Q!> q!> |         | "S>" is same as "n"
  #     J> j> J!> j!> |         | "L>" is same as "N"
  #                   |         |
  #     S< s< S!< s!< | Integer | same as the directives without "<" except
  #     L< l< L!< l!< |         | little endian
  #     I!< i!<       |         | (available since Ruby 1.9.3)
  #     Q< q< Q!< q!< |         | "S<" is same as "v"
  #     J< j< J!< j!< |         | "L<" is same as "V"
  #                   |         |
  #     n             | Integer | 16-bit unsigned, network (big-endian) byte order
  #     N             | Integer | 32-bit unsigned, network (big-endian) byte order
  #     v             | Integer | 16-bit unsigned, VAX (little-endian) byte order
  #     V             | Integer | 32-bit unsigned, VAX (little-endian) byte order
  #                   |         |
  #     U             | Integer | UTF-8 character
  #     w             | Integer | BER-compressed integer
  #
  #     Float        | Array   |
  #     Directive    | Element | Meaning
  #     ---------------------------------------------------------------------------
  #     D d          | Float   | double-precision, native format
  #     F f          | Float   | single-precision, native format
  #     E            | Float   | double-precision, little-endian byte order
  #     e            | Float   | single-precision, little-endian byte order
  #     G            | Float   | double-precision, network (big-endian) byte order
  #     g            | Float   | single-precision, network (big-endian) byte order
  #
  #     String       | Array   |
  #     Directive    | Element | Meaning
  #     ---------------------------------------------------------------------------
  #     A            | String  | arbitrary binary string (space padded, count is width)
  #     a            | String  | arbitrary binary string (null padded, count is width)
  #     Z            | String  | same as ``a'', except that null is added with *
  #     B            | String  | bit string (MSB first)
  #     b            | String  | bit string (LSB first)
  #     H            | String  | hex string (high nibble first)
  #     h            | String  | hex string (low nibble first)
  #     u            | String  | UU-encoded string
  #     M            | String  | quoted printable, MIME encoding (see also RFC2045)
  #                  |         | (text mode but input must use LF and output LF)
  #     m            | String  | base64 encoded string (see RFC 2045)
  #                  |         | (if count is 0, no line feed are added, see RFC 4648)
  #                  |         | (count specifies input bytes between each LF,
  #                  |         | rounded down to nearest multiple of 3)
  #     P            | String  | pointer to a structure (fixed-length string)
  #     p            | String  | pointer to a null-terminated string
  #
  #     Misc.        | Array   |
  #     Directive    | Element | Meaning
  #     ---------------------------------------------------------------------------
  #     @            | ---     | moves to absolute position
  #     X            | ---     | back up a byte
  #     x            | ---     | null byte
  #
  def pack: (string fmt, ?buffer: String?) -> String

  # When invoked with a block, yield all permutations of length `n` of the
  # elements of the array, then return the array itself.
  #
  # If `n` is not specified, yield all permutations of all elements.
  #
  # The implementation makes no guarantees about the order in which the
  # permutations are yielded.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  # Examples:
  #
  #     a = [1, 2, 3]
  #     a.permutation.to_a    #=> [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
  #     a.permutation(1).to_a #=> [[1],[2],[3]]
  #     a.permutation(2).to_a #=> [[1,2],[1,3],[2,1],[2,3],[3,1],[3,2]]
  #     a.permutation(3).to_a #=> [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
  #     a.permutation(0).to_a #=> [[]] # one permutation of length 0
  #     a.permutation(4).to_a #=> []   # no permutations of length 4
  #
  def permutation: (?int n) -> ::Enumerator[::Array[Elem], ::Array[Elem]]
                 | (?int n) { (::Array[Elem] p) -> void } -> ::Array[Elem]

  # Removes the last element from `self` and returns it, or `nil` if the array is
  # empty.
  #
  # If a number `n` is given, returns an array of the last `n` elements (or less)
  # just like `array.slice!(-n, n)` does. See also Array#push for the opposite
  # effect.
  #
  #     a = [ "a", "b", "c", "d" ]
  #     a.pop     #=> "d"
  #     a.pop(2)  #=> ["b", "c"]
  #     a         #=> ["a"]
  #
  def pop: () -> Elem?
         | (int n) -> ::Array[Elem]

  alias prepend unshift

  # Returns an array of all combinations of elements from all arrays.
  #
  # The length of the returned array is the product of the length of `self` and
  # the argument arrays.
  #
  # If given a block, #product will yield all combinations and return `self`
  # instead.
  #
  #     [1,2,3].product([4,5])     #=> [[1,4],[1,5],[2,4],[2,5],[3,4],[3,5]]
  #     [1,2].product([1,2])       #=> [[1,1],[1,2],[2,1],[2,2]]
  #     [1,2].product([3,4],[5,6]) #=> [[1,3,5],[1,3,6],[1,4,5],[1,4,6],
  #                                #     [2,3,5],[2,3,6],[2,4,5],[2,4,6]]
  #     [1,2].product()            #=> [[1],[2]]
  #     [1,2].product([])          #=> []
  #
  def product: () -> ::Array[[Elem]]
             | [X] (::Array[X] other_ary) -> ::Array[[Elem, X]]
             | [X, Y] (::Array[X] other_ary1, ::Array[Y] other_ary2) -> ::Array[[Elem, X, Y]]
             | [U] (*::Array[U] other_arys) -> ::Array[::Array[Elem | U]]

  # Append --- Pushes the given object(s) on to the end of this array. This
  # expression returns the array itself, so several appends may be chained
  # together. See also Array#pop for the opposite effect.
  #
  #     a = [ "a", "b", "c" ]
  #     a.push("d", "e", "f")
  #             #=> ["a", "b", "c", "d", "e", "f"]
  #     [1, 2, 3].push(4).push(5)
  #             #=> [1, 2, 3, 4, 5]
  #
  def push: (*Elem obj) -> self

  # Searches through the array whose elements are also arrays.
  #
  # Compares `obj` with the second element of each contained array using `obj.==`.
  #
  # Returns the first contained array that matches `obj`.
  #
  # See also Array#assoc.
  #
  #     a = [ [ 1, "one"], [2, "two"], [3, "three"], ["ii", "two"] ]
  #     a.rassoc("two")    #=> [2, "two"]
  #     a.rassoc("four")   #=> nil
  #
  alias rassoc assoc

  # Returns a new array containing the items in `self` for which the given block
  # is not `true`. The ordering of non-rejected elements is maintained.
  #
  # See also Array#delete_if
  #
  # If no block is given, an Enumerator is returned instead.
  #
  alias reject delete_if

  # Deletes every element of `self` for which the block evaluates to `true`, if no
  # changes were made returns `nil`.
  #
  # The array may not be changed instantly every time the block is called.
  #
  # See also Enumerable#reject and Array#delete_if.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  def reject!: () { (Elem item) -> boolish } -> self?
             | () -> ::Enumerator[Elem, self?]

  # When invoked with a block, yields all repeated combinations of length `n` of
  # elements from the array and then returns the array itself.
  #
  # The implementation makes no guarantees about the order in which the repeated
  # combinations are yielded.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  # Examples:
  #
  #     a = [1, 2, 3]
  #     a.repeated_combination(1).to_a  #=> [[1], [2], [3]]
  #     a.repeated_combination(2).to_a  #=> [[1,1],[1,2],[1,3],[2,2],[2,3],[3,3]]
  #     a.repeated_combination(3).to_a  #=> [[1,1,1],[1,1,2],[1,1,3],[1,2,2],[1,2,3],
  #                                     #    [1,3,3],[2,2,2],[2,2,3],[2,3,3],[3,3,3]]
  #     a.repeated_combination(4).to_a  #=> [[1,1,1,1],[1,1,1,2],[1,1,1,3],[1,1,2,2],[1,1,2,3],
  #                                     #    [1,1,3,3],[1,2,2,2],[1,2,2,3],[1,2,3,3],[1,3,3,3],
  #                                     #    [2,2,2,2],[2,2,2,3],[2,2,3,3],[2,3,3,3],[3,3,3,3]]
  #     a.repeated_combination(0).to_a  #=> [[]] # one combination of length 0
  #
  def repeated_combination: (int n) { (::Array[Elem] c) -> void } -> self
                          | (int n) -> ::Enumerator[::Array[Elem], self]

  # When invoked with a block, yield all repeated permutations of length `n` of
  # the elements of the array, then return the array itself.
  #
  # The implementation makes no guarantees about the order in which the repeated
  # permutations are yielded.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  # Examples:
  #
  #     a = [1, 2]
  #     a.repeated_permutation(1).to_a  #=> [[1], [2]]
  #     a.repeated_permutation(2).to_a  #=> [[1,1],[1,2],[2,1],[2,2]]
  #     a.repeated_permutation(3).to_a  #=> [[1,1,1],[1,1,2],[1,2,1],[1,2,2],
  #                                     #    [2,1,1],[2,1,2],[2,2,1],[2,2,2]]
  #     a.repeated_permutation(0).to_a  #=> [[]] # one permutation of length 0
  #
  def repeated_permutation: (int n) { (::Array[Elem] p) -> void } -> self
                          | (int n) -> ::Enumerator[::Array[Elem], self]

  # Replaces the contents of `self` with the contents of `other_ary`, truncating
  # or expanding if necessary.
  #
  #     a = [ "a", "b", "c", "d", "e" ]
  #     a.replace([ "x", "y", "z" ])   #=> ["x", "y", "z"]
  #     a                              #=> ["x", "y", "z"]
  #
  def replace: (::Array[Elem]) -> self

  # Returns a new array containing `self`'s elements in reverse order.
  #
  #     [ "a", "b", "c" ].reverse   #=> ["c", "b", "a"]
  #     [ 1 ].reverse               #=> [1]
  #
  def reverse: () -> ::Array[Elem]

  # Reverses `self` in place.
  #
  #     a = [ "a", "b", "c" ]
  #     a.reverse!       #=> ["c", "b", "a"]
  #     a                #=> ["c", "b", "a"]
  #
  def reverse!: () -> ::Array[Elem]

  # Same as Array#each, but traverses `self` in reverse order.
  #
  #     a = [ "a", "b", "c" ]
  #     a.reverse_each {|x| print x, " " }
  #
  # produces:
  #
  #     c b a
  #
  def reverse_each: () { (Elem item) -> void } -> self
                  | () -> ::Enumerator[Elem, self]

  # Returns the *index* of the last object in `self` `==` to `obj`.
  #
  # If a block is given instead of an argument, returns the *index* of the first
  # object for which the block returns `true`, starting from the last object.
  #
  # Returns `nil` if no match is found.
  #
  # See also Array#index.
  #
  # If neither block nor argument is given, an Enumerator is returned instead.
  #
  #     a = [ "a", "b", "b", "b", "c" ]
  #     a.rindex("b")             #=> 3
  #     a.rindex("z")             #=> nil
  #     a.rindex {|x| x == "b"}   #=> 3
  #
  def rindex: (untyped obj) -> ::Integer?
            | () { (Elem item) -> boolish } -> ::Integer?
            | () -> ::Enumerator[Elem, ::Integer?]

  # Returns a new array by rotating `self` so that the element at `count` is the
  # first element of the new array.
  #
  # If `count` is negative then it rotates in the opposite direction, starting
  # from the end of `self` where `-1` is the last element.
  #
  #     a = [ "a", "b", "c", "d" ]
  #     a.rotate         #=> ["b", "c", "d", "a"]
  #     a                #=> ["a", "b", "c", "d"]
  #     a.rotate(2)      #=> ["c", "d", "a", "b"]
  #     a.rotate(-3)     #=> ["b", "c", "d", "a"]
  #
  def rotate: (?int count) -> ::Array[Elem]

  # Rotates `self` in place so that the element at `count` comes first, and
  # returns `self`.
  #
  # If `count` is negative then it rotates in the opposite direction, starting
  # from the end of the array where `-1` is the last element.
  #
  #     a = [ "a", "b", "c", "d" ]
  #     a.rotate!        #=> ["b", "c", "d", "a"]
  #     a                #=> ["b", "c", "d", "a"]
  #     a.rotate!(2)     #=> ["d", "a", "b", "c"]
  #     a.rotate!(-3)    #=> ["a", "b", "c", "d"]
  #
  def rotate!: (?int count) -> self

  # Choose a random element or `n` random elements from the array.
  #
  # The elements are chosen by using random and unique indices into the array in
  # order to ensure that an element doesn't repeat itself unless the array already
  # contained duplicate elements.
  #
  # If the array is empty the first form returns `nil` and the second form returns
  # an empty array.
  #
  #     a = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ]
  #     a.sample         #=> 7
  #     a.sample(4)      #=> [6, 4, 2, 5]
  #
  # The optional `rng` argument will be used as the random number generator.
  #
  #     a.sample(random: Random.new(1))     #=> 6
  #     a.sample(4, random: Random.new(1))  #=> [6, 10, 9, 2]
  #
  def sample: (?random: Random rng) -> Elem?
            | (?int n, ?random: Random rng) -> ::Array[Elem]

  # Returns a new array containing all elements of `ary` for which the given
  # `block` returns a true value.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  #     [1,2,3,4,5].select {|num| num.even? }     #=> [2, 4]
  #
  #     a = %w[ a b c d e f ]
  #     a.select {|v| v =~ /[aeiou]/ }    #=> ["a", "e"]
  #
  # See also Enumerable#select.
  #
  # Array#filter is an alias for Array#select.
  #
  def select: () { (Elem item) -> boolish } -> ::Array[Elem]
            | () -> ::Enumerator[Elem, ::Array[Elem]]

  # Invokes the given block passing in successive elements from `self`, deleting
  # elements for which the block returns a `false` value.
  #
  # The array may not be changed instantly every time the block is called.
  #
  # If changes were made, it will return `self`, otherwise it returns `nil`.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  # See also Array#keep_if.
  #
  # Array#filter! is an alias for Array#select!.
  #
  def select!: () { (Elem item) -> boolish } -> self?
             | () -> ::Enumerator[Elem, self?]

  # Removes the first element of `self` and returns it (shifting all other
  # elements down by one). Returns `nil` if the array is empty.
  #
  # If a number `n` is given, returns an array of the first `n` elements (or less)
  # just like `array.slice!(0, n)` does. With `ary` containing only the remainder
  # elements, not including what was shifted to `new_ary`. See also Array#unshift
  # for the opposite effect.
  #
  #     args = [ "-m", "-q", "filename" ]
  #     args.shift     #=> "-m"
  #     args           #=> ["-q", "filename"]
  #
  #     args = [ "-m", "-q", "filename" ]
  #     args.shift(2)  #=> ["-m", "-q"]
  #     args           #=> ["filename"]
  #
  def shift: () -> Elem?
           | (?int n) -> ::Array[Elem]

  # Returns a new array with elements of `self` shuffled.
  #
  #     a = [ 1, 2, 3 ]           #=> [1, 2, 3]
  #     a.shuffle                 #=> [2, 3, 1]
  #     a                         #=> [1, 2, 3]
  #
  # The optional `rng` argument will be used as the random number generator.
  #
  #     a.shuffle(random: Random.new(1))  #=> [1, 3, 2]
  #
  def shuffle: (?random: Random rng) -> ::Array[Elem]

  # Shuffles elements in `self` in place.
  #
  #     a = [ 1, 2, 3 ]           #=> [1, 2, 3]
  #     a.shuffle!                #=> [2, 3, 1]
  #     a                         #=> [2, 3, 1]
  #
  # The optional `rng` argument will be used as the random number generator.
  #
  #     a.shuffle!(random: Random.new(1))  #=> [1, 3, 2]
  #
  def shuffle!: (?random: Random rng) -> self

  alias size length

  # Element Reference --- Returns the element at `index`, or returns a subarray
  # starting at the `start` index and continuing for `length` elements, or returns
  # a subarray specified by `range` of indices.
  #
  # Negative indices count backward from the end of the array (-1 is the last
  # element).  For `start` and `range` cases the starting index is just before an
  # element.  Additionally, an empty array is returned when the starting index for
  # an element range is at the end of the array.
  #
  # Returns `nil` if the index (or starting index) are out of range.
  #
  #     a = [ "a", "b", "c", "d", "e" ]
  #     a[2] +  a[0] + a[1]    #=> "cab"
  #     a[6]                   #=> nil
  #     a[1, 2]                #=> [ "b", "c" ]
  #     a[1..3]                #=> [ "b", "c", "d" ]
  #     a[4..7]                #=> [ "e" ]
  #     a[6..10]               #=> nil
  #     a[-3, 3]               #=> [ "c", "d", "e" ]
  #     # special cases
  #     a[5]                   #=> nil
  #     a[6, 1]                #=> nil
  #     a[5, 1]                #=> []
  #     a[5..10]               #=> []
  #
  def slice: (int index) -> Elem?
           | (int start, int length) -> ::Array[Elem]?
           | (::Range[::Integer] range) -> ::Array[Elem]?

  # Deletes the element(s) given by an `index` (optionally up to `length`
  # elements) or by a `range`.
  #
  # Returns the deleted object (or objects), or `nil` if the `index` is out of
  # range.
  #
  #     a = [ "a", "b", "c" ]
  #     a.slice!(1)     #=> "b"
  #     a               #=> ["a", "c"]
  #     a.slice!(-1)    #=> "c"
  #     a               #=> ["a"]
  #     a.slice!(100)   #=> nil
  #     a               #=> ["a"]
  #
  def slice!: (int index) -> Elem?
            | (int start, int length) -> ::Array[Elem]?
            | (::Range[::Integer] range) -> ::Array[Elem]?

  # Returns a new array created by sorting `self`.
  #
  # Comparisons for the sort will be done using the `<=>` operator or using an
  # optional code block.
  #
  # The block must implement a comparison between `a` and `b` and return an
  # integer less than 0 when `b` follows `a`, `0` when `a` and `b` are equivalent,
  # or an integer greater than 0 when `a` follows `b`.
  #
  # The result is not guaranteed to be stable.  When the comparison of two
  # elements returns `0`, the order of the elements is unpredictable.
  #
  #     ary = [ "d", "a", "e", "c", "b" ]
  #     ary.sort                     #=> ["a", "b", "c", "d", "e"]
  #     ary.sort {|a, b| b <=> a}    #=> ["e", "d", "c", "b", "a"]
  #
  # To produce the reverse order, the following can also be used (and may be
  # faster):
  #
  #     ary.sort.reverse!             #=> ["e", "d", "c", "b", "a"]
  #
  # See also Enumerable#sort_by.
  #
  def sort: () -> ::Array[Elem]
          | () { (Elem a, Elem b) -> ::Integer? } -> ::Array[Elem]

  # Sorts `self` in place.
  #
  # Comparisons for the sort will be done using the `<=>` operator or using an
  # optional code block.
  #
  # The block must implement a comparison between `a` and `b` and return an
  # integer less than 0 when `b` follows `a`, `0` when `a` and `b` are equivalent,
  # or an integer greater than 0 when `a` follows `b`.
  #
  # The result is not guaranteed to be stable.  When the comparison of two
  # elements returns `0`, the order of the elements is unpredictable.
  #
  #     ary = [ "d", "a", "e", "c", "b" ]
  #     ary.sort!                     #=> ["a", "b", "c", "d", "e"]
  #     ary.sort! {|a, b| b <=> a}    #=> ["e", "d", "c", "b", "a"]
  #
  # See also Enumerable#sort_by.
  #
  def sort!: () -> self
           | () { (Elem a, Elem b) -> ::Integer? } -> self

  # Sorts `self` in place using a set of keys generated by mapping the values in
  # `self` through the given block.
  #
  # The result is not guaranteed to be stable.  When two keys are equal, the order
  # of the corresponding elements is unpredictable.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  # See also Enumerable#sort_by.
  #
  def sort_by!: [U] () { (Elem obj) -> U } -> ::Array[Elem]
              | () -> ::Enumerator[Elem, ::Array[Elem]]

  # Returns the sum of elements. For example, [e1, e2, e3].sum returns init + e1 +
  # e2 + e3.
  #
  # If a block is given, the block is applied to each element before addition.
  #
  # If *ary* is empty, it returns *init*.
  #
  #     [].sum                             #=> 0
  #     [].sum(0.0)                        #=> 0.0
  #     [1, 2, 3].sum                      #=> 6
  #     [3, 5.5].sum                       #=> 8.5
  #     [2.5, 3.0].sum(0.0) {|e| e * e }   #=> 15.25
  #     [Object.new].sum                   #=> TypeError
  #
  # The (arithmetic) mean value of an array can be obtained as follows.
  #
  #     mean = ary.sum(0.0) / ary.length
  #
  # This method can be used for non-numeric objects by explicit *init* argument.
  #
  #     ["a", "b", "c"].sum("")            #=> "abc"
  #     [[1], [[2]], [3]].sum([])          #=> [1, [2], 3]
  #
  # However, Array#join and Array#flatten is faster than Array#sum for array of
  # strings and array of arrays.
  #
  #     ["a", "b", "c"].join               #=> "abc"
  #     [[1], [[2]], [3]].flatten(1)       #=> [1, [2], 3]
  #
  # Array#sum method may not respect method redefinition of "+" methods such as
  # Integer#+.
  #
  def sum: (?untyped init) -> untyped
         | (?untyped init) { (Elem e) -> untyped } -> untyped

  # Returns first `n` elements from the array.
  #
  # If a negative number is given, raises an ArgumentError.
  #
  # See also Array#drop
  #
  #     a = [1, 2, 3, 4, 5, 0]
  #     a.take(3)             #=> [1, 2, 3]
  #
  def take: (int n) -> ::Array[Elem]

  # Passes elements to the block until the block returns `nil` or `false`, then
  # stops iterating and returns an array of all prior elements.
  #
  # If no block is given, an Enumerator is returned instead.
  #
  # See also Array#drop_while
  #
  #     a = [1, 2, 3, 4, 5, 0]
  #     a.take_while {|i| i < 3}    #=> [1, 2]
  #
  def take_while: () { (Elem obj) -> boolish } -> ::Array[Elem]
                | () -> ::Enumerator[Elem, ::Array[Elem]]

  # Returns `self`.
  #
  # If called on a subclass of Array, converts the receiver to an Array object.
  #
  def to_a: () -> ::Array[Elem]

  # Returns `self`.
  #
  def to_ary: () -> self

  # Returns the result of interpreting *ary* as an array of `[key, value]` pairs.
  #
  #     [[:foo, :bar], [1, 2]].to_h
  #       # => {:foo => :bar, 1 => 2}
  #
  # If a block is given, the results of the block on each element of the array
  # will be used as pairs.
  #
  #     ["foo", "bar"].to_h {|s| [s.ord, s]}
  #       # => {102=>"foo", 98=>"bar"}
  #
  def to_h: () -> Hash[untyped, untyped]
          | [T, S] () { (Elem) -> [T, S] } -> Hash[T, S]

  alias to_s inspect

  # Assumes that `self` is an array of arrays and transposes the rows and columns.
  #
  #     a = [[1,2], [3,4], [5,6]]
  #     a.transpose   #=> [[1, 3, 5], [2, 4, 6]]
  #
  # If the length of the subarrays don't match, an IndexError is raised.
  #
  def transpose: () -> ::Array[::Array[untyped]]

  # Set Union --- Returns a new array by joining `other_ary`s with `self`,
  # excluding any duplicates and preserving the order from the given arrays.
  #
  # It compares elements using their #hash and #eql? methods for efficiency.
  #
  #     [ "a", "b", "c" ].union( [ "c", "d", "a" ] )    #=> [ "a", "b", "c", "d" ]
  #     [ "a" ].union( ["e", "b"], ["a", "c", "b"] )    #=> [ "a", "e", "b", "c" ]
  #     [ "a" ].union #=> [ "a" ]
  #
  # See also Array#|.
  #
  def union: [T] (*::Array[T] other_arys) -> ::Array[T | Elem]

  # Returns a new array by removing duplicate values in `self`.
  #
  # If a block is given, it will use the return value of the block for comparison.
  #
  # It compares values using their #hash and #eql? methods for efficiency.
  #
  # `self` is traversed in order, and the first occurrence is kept.
  #
  #     a = [ "a", "a", "b", "b", "c" ]
  #     a.uniq   # => ["a", "b", "c"]
  #
  #     b = [["student","sam"], ["student","george"], ["teacher","matz"]]
  #     b.uniq {|s| s.first}   # => [["student", "sam"], ["teacher", "matz"]]
  #
  def uniq: () -> ::Array[Elem]
          | () { (Elem item) -> untyped } -> ::Array[Elem]

  # Removes duplicate elements from `self`.
  #
  # If a block is given, it will use the return value of the block for comparison.
  #
  # It compares values using their #hash and #eql? methods for efficiency.
  #
  # `self` is traversed in order, and the first occurrence is kept.
  #
  # Returns `nil` if no changes are made (that is, no duplicates are found).
  #
  #     a = [ "a", "a", "b", "b", "c" ]
  #     a.uniq!   # => ["a", "b", "c"]
  #
  #     b = [ "a", "b", "c" ]
  #     b.uniq!   # => nil
  #
  #     c = [["student","sam"], ["student","george"], ["teacher","matz"]]
  #     c.uniq! {|s| s.first}   # => [["student", "sam"], ["teacher", "matz"]]
  #
  def uniq!: () -> self?
           | () { (Elem) -> untyped } -> self?

  # Prepends objects to the front of `self`, moving other elements upwards. See
  # also Array#shift for the opposite effect.
  #
  #     a = [ "b", "c", "d" ]
  #     a.unshift("a")   #=> ["a", "b", "c", "d"]
  #     a.unshift(1, 2)  #=> [ 1, 2, "a", "b", "c", "d"]
  #
  def unshift: (*Elem obj) -> self

  # Returns an array containing the elements in `self` corresponding to the given
  # `selector`(s).
  #
  # The selectors may be either integer indices or ranges.
  #
  # See also Array#select.
  #
  #     a = %w{ a b c d e f }
  #     a.values_at(1, 3, 5)          # => ["b", "d", "f"]
  #     a.values_at(1, 3, 5, 7)       # => ["b", "d", "f", nil]
  #     a.values_at(-1, -2, -2, -7)   # => ["f", "e", "e", nil]
  #     a.values_at(4..6, 3...6)      # => ["e", "f", nil, "d", "e", "f"]
  #
  def values_at: (*int | ::Range[::Integer] selector) -> ::Array[Elem?]

  # Converts any arguments to arrays, then merges elements of `self` with
  # corresponding elements from each argument.
  #
  # This generates a sequence of `ary.size` *n*-element arrays, where *n* is one
  # more than the count of arguments.
  #
  # If the size of any argument is less than the size of the initial array, `nil`
  # values are supplied.
  #
  # If a block is given, it is invoked for each output `array`, otherwise an array
  # of arrays is returned.
  #
  #     a = [ 4, 5, 6 ]
  #     b = [ 7, 8, 9 ]
  #     [1, 2, 3].zip(a, b)   #=> [[1, 4, 7], [2, 5, 8], [3, 6, 9]]
  #     [1, 2].zip(a, b)      #=> [[1, 4, 7], [2, 5, 8]]
  #     a.zip([1, 2], [8])    #=> [[4, 1, 8], [5, 2, nil], [6, nil, nil]]
  #
  def zip: [U] (::Array[U] arg) -> ::Array[[ Elem, U? ]]
         | (::Array[untyped] arg, *::Array[untyped] args) -> ::Array[::Array[untyped]]
         | [U] (::Array[U] arg) { ([Elem, U?]) -> void } -> void
         | (::Array[untyped] arg, *::Array[untyped] args) { (::Array[untyped]) -> void } -> void

  # Set Union --- Returns a new array by joining `ary` with `other_ary`, excluding
  # any duplicates and preserving the order from the given arrays.
  #
  # It compares elements using their #hash and #eql? methods for efficiency.
  #
  #     [ "a", "b", "c" ] | [ "c", "d", "a" ]    #=> [ "a", "b", "c", "d" ]
  #     [ "c", "d", "a" ] | [ "a", "b", "c" ]    #=> [ "c", "d", "a", "b" ]
  #
  # See also Array#union.
  #
  def |: [T] (::Array[T] other_ary) -> ::Array[Elem | T]

  private

  # Replaces the contents of `self` with the contents of `other_ary`, truncating
  # or expanding if necessary.
  #
  #     a = [ "a", "b", "c", "d", "e" ]
  #     a.replace([ "x", "y", "z" ])   #=> ["x", "y", "z"]
  #     a                              #=> ["x", "y", "z"]
  #
  def initialize_copy: (self other_ary) -> void
end

interface _ToA[T]
  def to_a: () -> Array[T]
end

interface _ToAry[T]
  def to_ary: () -> ::Array[T]
end

interface Array::_Pattern[T]
  def ===: (T) -> bool
end