diff --git a/src/doc/unstable-book/src/library-features/fnbox.md b/src/doc/unstable-book/src/library-features/fnbox.md
new file mode 100644
index 0000000000000..cb3386b715211
--- /dev/null
+++ b/src/doc/unstable-book/src/library-features/fnbox.md
@@ -0,0 +1,32 @@
+# `fnbox`
+
+The tracking issue for this feature is [#28796]
+
+[#28796]: https://github.com/rust-lang/rust/issues/28796
+
+------------------------
+
+This had been a temporary alternative to the following impls:
+
+```rust,ignore
+impl<A, F> FnOnce for Box<F> where F: FnOnce<A> + ?Sized {}
+impl<A, F> FnMut for Box<F> where F: FnMut<A> + ?Sized {}
+impl<A, F> Fn for Box<F> where F: Fn<A> + ?Sized {}
+```
+
+The impls are parallel to these (relatively old) impls:
+
+```rust,ignore
+impl<A, F> FnOnce for &mut F where F: FnMut<A> + ?Sized {}
+impl<A, F> FnMut for &mut F where F: FnMut<A> + ?Sized {}
+impl<A, F> Fn for &mut F where F: Fn<A> + ?Sized {}
+impl<A, F> FnOnce for &F where F: Fn<A> + ?Sized {}
+impl<A, F> FnMut for &F where F: Fn<A> + ?Sized {}
+impl<A, F> Fn for &F where F: Fn<A> + ?Sized {}
+```
+
+Before the introduction of [`unsized_locals`][unsized_locals], we had been unable to provide the former impls. That means, unlike `&dyn Fn()` or `&mut dyn FnMut()` we could not use `Box<dyn FnOnce()>` at that time.
+
+[unsized_locals]: language-features/unsized-locals.html
+
+`FnBox()` is an alternative approach to `Box<dyn FnBox()>` is delegated to `FnBox::call_box` which doesn't need unsized locals. As we now have `Box<dyn FnOnce()>` working, the `fnbox` feature is going to be removed.
diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index b2315c6a73907..f6dee7c9eefd6 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -694,6 +694,28 @@ impl<I: ExactSizeIterator + ?Sized> ExactSizeIterator for Box<I> {
#[stable(feature = "fused", since = "1.26.0")]
impl<I: FusedIterator + ?Sized> FusedIterator for Box<I> {}
+#[stable(feature = "boxed_closure_impls", since = "1.35.0")]
+impl<A, F: FnOnce<A> + ?Sized> FnOnce<A> for Box<F> {
+ type Output = <F as FnOnce<A>>::Output;
+
+ extern "rust-call" fn call_once(self, args: A) -> Self::Output {
+ <F as FnOnce<A>>::call_once(*self, args)
+ }
+}
+
+#[stable(feature = "boxed_closure_impls", since = "1.35.0")]
+impl<A, F: FnMut<A> + ?Sized> FnMut<A> for Box<F> {
+ extern "rust-call" fn call_mut(&mut self, args: A) -> Self::Output {
+ <F as FnMut<A>>::call_mut(self, args)
+ }
+}
+
+#[stable(feature = "boxed_closure_impls", since = "1.35.0")]
+impl<A, F: Fn<A> + ?Sized> Fn<A> for Box<F> {
+ extern "rust-call" fn call(&self, args: A) -> Self::Output {
+ <F as Fn<A>>::call(self, args)
+ }
+}
/// `FnBox` is a version of the `FnOnce` intended for use with boxed
/// closure objects. The idea is that where one would normally store a
@@ -735,9 +757,7 @@ impl<I: FusedIterator + ?Sized> FusedIterator for Box<I> {}
#[rustc_paren_sugar]
#[unstable(feature = "fnbox",
reason = "will be deprecated if and when `Box<FnOnce>` becomes usable", issue = "28796")]
-pub trait FnBox<A> {
- type Output;
-
+pub trait FnBox<A>: FnOnce<A> {
fn call_box(self: Box<Self>, args: A) -> Self::Output;
}
@@ -746,33 +766,11 @@ pub trait FnBox<A> {
impl<A, F> FnBox<A> for F
where F: FnOnce<A>
{
- type Output = F::Output;
-
fn call_box(self: Box<F>, args: A) -> F::Output {
self.call_once(args)
}
}
-#[unstable(feature = "fnbox",
- reason = "will be deprecated if and when `Box<FnOnce>` becomes usable", issue = "28796")]
-impl<A, R> FnOnce<A> for Box<dyn FnBox<A, Output = R> + '_> {
- type Output = R;
-
- extern "rust-call" fn call_once(self, args: A) -> R {
- self.call_box(args)
- }
-}
-
-#[unstable(feature = "fnbox",
- reason = "will be deprecated if and when `Box<FnOnce>` becomes usable", issue = "28796")]
-impl<A, R> FnOnce<A> for Box<dyn FnBox<A, Output = R> + Send + '_> {
- type Output = R;
-
- extern "rust-call" fn call_once(self, args: A) -> R {
- self.call_box(args)
- }
-}
-
#[unstable(feature = "coerce_unsized", issue = "27732")]
impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Box<U>> for Box<T> {}
diff --git a/src/liballoc/lib.rs b/src/liballoc/lib.rs
index 90ff56814fbb1..9064b4ccd6a88 100644
--- a/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@ -107,6 +107,7 @@
#![feature(unboxed_closures)]
#![feature(unicode_internals)]
#![feature(unsize)]
+#![feature(unsized_locals)]
#![feature(allocator_internals)]
#![feature(on_unimplemented)]
#![feature(rustc_const_unstable)]
diff --git a/src/test/run-pass/unsized-locals/box-fnonce.rs b/src/test/run-pass/unsized-locals/box-fnonce.rs
new file mode 100644
index 0000000000000..16bdeae4fad41
--- /dev/null
+++ b/src/test/run-pass/unsized-locals/box-fnonce.rs
@@ -0,0 +1,8 @@
+fn call_it<T>(f: Box<dyn FnOnce() -> T>) -> T {
+ f()
+}
+
+fn main() {
+ let s = "hello".to_owned();
+ assert_eq!(&call_it(Box::new(|| s)) as &str, "hello");
+}
diff --git a/src/test/run-pass/unsized-locals/fnbox-compat.rs b/src/test/run-pass/unsized-locals/fnbox-compat.rs
new file mode 100644
index 0000000000000..5ec54ada13bb0
--- /dev/null
+++ b/src/test/run-pass/unsized-locals/fnbox-compat.rs
@@ -0,0 +1,12 @@
+#![feature(fnbox)]
+
+use std::boxed::FnBox;
+
+fn call_it<T>(f: Box<dyn FnBox() -> T>) -> T {
+ f()
+}
+
+fn main() {
+ let s = "hello".to_owned();
+ assert_eq!(&call_it(Box::new(|| s)) as &str, "hello");
+}
diff --git a/src/test/ui/borrowck/two-phase-nonrecv-autoref.ast.nll.stderr b/src/test/ui/borrowck/two-phase-nonrecv-autoref.ast.nll.stderr
index d026f81b7aad6..223de36f0df31 100644
--- a/src/test/ui/borrowck/two-phase-nonrecv-autoref.ast.nll.stderr
+++ b/src/test/ui/borrowck/two-phase-nonrecv-autoref.ast.nll.stderr
@@ -7,17 +7,15 @@ LL | f(f(10));
| first mutable borrow occurs here
| first borrow later used by call
-error[E0382]: use of moved value: `*f`
+error[E0382]: use of moved value: `f`
--> $DIR/two-phase-nonrecv-autoref.rs:69:11
|
LL | fn twice_ten_so<F: FnOnce(i32) -> i32>(f: Box<F>) {
- | - consider adding a `Copy` constraint to this type argument
+ | - move occurs because `f` has type `std::boxed::Box<F>`, which does not implement the `Copy` trait
LL | f(f(10));
| - ^ value used here after move
| |
| value moved here
- |
- = note: move occurs because `*f` has type `F`, which does not implement the `Copy` trait
error[E0499]: cannot borrow `*f` as mutable more than once at a time
--> $DIR/two-phase-nonrecv-autoref.rs:76:11
@@ -28,30 +26,18 @@ LL | f(f(10));
| first mutable borrow occurs here
| first borrow later used by call
-error[E0161]: cannot move a value of type dyn std::ops::FnOnce(i32) -> i32: the size of dyn std::ops::FnOnce(i32) -> i32 cannot be statically determined
- --> $DIR/two-phase-nonrecv-autoref.rs:85:9
- |
-LL | f(f(10));
- | ^
-
-error[E0161]: cannot move a value of type dyn std::ops::FnOnce(i32) -> i32: the size of dyn std::ops::FnOnce(i32) -> i32 cannot be statically determined
- --> $DIR/two-phase-nonrecv-autoref.rs:85:11
- |
-LL | f(f(10));
- | ^
-
-error[E0382]: use of moved value: `*f`
+error[E0382]: use of moved value: `f`
--> $DIR/two-phase-nonrecv-autoref.rs:85:11
|
+LL | fn twice_ten_oo(f: Box<FnOnce(i32) -> i32>) {
+ | - move occurs because `f` has type `std::boxed::Box<dyn std::ops::FnOnce(i32) -> i32>`, which does not implement the `Copy` trait
LL | f(f(10));
| - ^ value used here after move
| |
| value moved here
- |
- = note: move occurs because `*f` has type `dyn std::ops::FnOnce(i32) -> i32`, which does not implement the `Copy` trait
error[E0502]: cannot borrow `a` as immutable because it is also borrowed as mutable
- --> $DIR/two-phase-nonrecv-autoref.rs:129:27
+ --> $DIR/two-phase-nonrecv-autoref.rs:125:27
|
LL | double_access(&mut a, &a);
| ------------- ------ ^^ immutable borrow occurs here
@@ -60,7 +46,7 @@ LL | double_access(&mut a, &a);
| mutable borrow later used by call
error[E0502]: cannot borrow `i` as immutable because it is also borrowed as mutable
- --> $DIR/two-phase-nonrecv-autoref.rs:157:7
+ --> $DIR/two-phase-nonrecv-autoref.rs:153:7
|
LL | i[i[3]] = 4;
| --^----
@@ -70,7 +56,7 @@ LL | i[i[3]] = 4;
| mutable borrow later used here
error[E0502]: cannot borrow `i` as immutable because it is also borrowed as mutable
- --> $DIR/two-phase-nonrecv-autoref.rs:163:7
+ --> $DIR/two-phase-nonrecv-autoref.rs:159:7
|
LL | i[i[3]] = i[4];
| --^----
@@ -79,7 +65,7 @@ LL | i[i[3]] = i[4];
| mutable borrow occurs here
| mutable borrow later used here
-error: aborting due to 9 previous errors
+error: aborting due to 7 previous errors
-Some errors occurred: E0161, E0382, E0499, E0502.
-For more information about an error, try `rustc --explain E0161`.
+Some errors occurred: E0382, E0499, E0502.
+For more information about an error, try `rustc --explain E0382`.
diff --git a/src/test/ui/borrowck/two-phase-nonrecv-autoref.ast.stderr b/src/test/ui/borrowck/two-phase-nonrecv-autoref.ast.stderr
index 426939f371ca5..d98b272944fdc 100644
--- a/src/test/ui/borrowck/two-phase-nonrecv-autoref.ast.stderr
+++ b/src/test/ui/borrowck/two-phase-nonrecv-autoref.ast.stderr
@@ -15,7 +15,7 @@ LL | f(f(10));
| | second mutable borrow occurs here
| first mutable borrow occurs here
-error[E0382]: use of moved value: `*f`
+error[E0382]: use of moved value: `f`
--> $DIR/two-phase-nonrecv-autoref.rs:69:11
|
LL | f(f(10));
@@ -23,7 +23,7 @@ LL | f(f(10));
| |
| value moved here
|
- = note: move occurs because `*f` has type `F`, which does not implement the `Copy` trait
+ = note: move occurs because `f` has type `std::boxed::Box<F>`, which does not implement the `Copy` trait
error[E0499]: cannot borrow `*f` as mutable more than once at a time
--> $DIR/two-phase-nonrecv-autoref.rs:76:11
@@ -34,7 +34,7 @@ LL | f(f(10));
| | second mutable borrow occurs here
| first mutable borrow occurs here
-error[E0382]: use of moved value: `*f`
+error[E0382]: use of moved value: `f`
--> $DIR/two-phase-nonrecv-autoref.rs:85:11
|
LL | f(f(10));
@@ -42,10 +42,10 @@ LL | f(f(10));
| |
| value moved here
|
- = note: move occurs because `*f` has type `(dyn std::ops::FnOnce(i32) -> i32 + 'static)`, which does not implement the `Copy` trait
+ = note: move occurs because `f` has type `std::boxed::Box<(dyn std::ops::FnOnce(i32) -> i32 + 'static)>`, which does not implement the `Copy` trait
error[E0502]: cannot borrow `a` as immutable because it is also borrowed as mutable
- --> $DIR/two-phase-nonrecv-autoref.rs:129:28
+ --> $DIR/two-phase-nonrecv-autoref.rs:125:28
|
LL | double_access(&mut a, &a);
| - ^- mutable borrow ends here
@@ -54,7 +54,7 @@ LL | double_access(&mut a, &a);
| mutable borrow occurs here
error[E0502]: cannot borrow `a` as immutable because it is also borrowed as mutable
- --> $DIR/two-phase-nonrecv-autoref.rs:135:9
+ --> $DIR/two-phase-nonrecv-autoref.rs:131:9
|
LL | a.m(a.i(10));
| - ^ - mutable borrow ends here
@@ -63,7 +63,7 @@ LL | a.m(a.i(10));
| mutable borrow occurs here
error[E0502]: cannot borrow `i` as immutable because it is also borrowed as mutable
- --> $DIR/two-phase-nonrecv-autoref.rs:157:7
+ --> $DIR/two-phase-nonrecv-autoref.rs:153:7
|
LL | i[i[3]] = 4;
| - ^ - mutable borrow ends here
@@ -72,7 +72,7 @@ LL | i[i[3]] = 4;
| mutable borrow occurs here
error[E0502]: cannot borrow `i` as immutable because it is also borrowed as mutable
- --> $DIR/two-phase-nonrecv-autoref.rs:163:7
+ --> $DIR/two-phase-nonrecv-autoref.rs:159:7
|
LL | i[i[3]] = i[4];
| - ^ - mutable borrow ends here
@@ -81,7 +81,7 @@ LL | i[i[3]] = i[4];
| mutable borrow occurs here
error[E0502]: cannot borrow `v` as immutable because it is also borrowed as mutable
- --> $DIR/two-phase-nonrecv-autoref.rs:172:12
+ --> $DIR/two-phase-nonrecv-autoref.rs:168:12
|
LL | v.push(v.len());
| - ^ - mutable borrow ends here
@@ -90,7 +90,7 @@ LL | v.push(v.len());
| mutable borrow occurs here
error[E0502]: cannot borrow `s` as immutable because it is also borrowed as mutable
- --> $DIR/two-phase-nonrecv-autoref.rs:183:9
+ --> $DIR/two-phase-nonrecv-autoref.rs:179:9
|
LL | s.m(s.i(10));
| - ^ - mutable borrow ends here
@@ -99,7 +99,7 @@ LL | s.m(s.i(10));
| mutable borrow occurs here
error[E0502]: cannot borrow `t` as immutable because it is also borrowed as mutable
- --> $DIR/two-phase-nonrecv-autoref.rs:188:9
+ --> $DIR/two-phase-nonrecv-autoref.rs:184:9
|
LL | t.m(t.i(10));
| - ^ - mutable borrow ends here
diff --git a/src/test/ui/borrowck/two-phase-nonrecv-autoref.nll.stderr b/src/test/ui/borrowck/two-phase-nonrecv-autoref.nll.stderr
index d026f81b7aad6..223de36f0df31 100644
--- a/src/test/ui/borrowck/two-phase-nonrecv-autoref.nll.stderr
+++ b/src/test/ui/borrowck/two-phase-nonrecv-autoref.nll.stderr
@@ -7,17 +7,15 @@ LL | f(f(10));
| first mutable borrow occurs here
| first borrow later used by call
-error[E0382]: use of moved value: `*f`
+error[E0382]: use of moved value: `f`
--> $DIR/two-phase-nonrecv-autoref.rs:69:11
|
LL | fn twice_ten_so<F: FnOnce(i32) -> i32>(f: Box<F>) {
- | - consider adding a `Copy` constraint to this type argument
+ | - move occurs because `f` has type `std::boxed::Box<F>`, which does not implement the `Copy` trait
LL | f(f(10));
| - ^ value used here after move
| |
| value moved here
- |
- = note: move occurs because `*f` has type `F`, which does not implement the `Copy` trait
error[E0499]: cannot borrow `*f` as mutable more than once at a time
--> $DIR/two-phase-nonrecv-autoref.rs:76:11
@@ -28,30 +26,18 @@ LL | f(f(10));
| first mutable borrow occurs here
| first borrow later used by call
-error[E0161]: cannot move a value of type dyn std::ops::FnOnce(i32) -> i32: the size of dyn std::ops::FnOnce(i32) -> i32 cannot be statically determined
- --> $DIR/two-phase-nonrecv-autoref.rs:85:9
- |
-LL | f(f(10));
- | ^
-
-error[E0161]: cannot move a value of type dyn std::ops::FnOnce(i32) -> i32: the size of dyn std::ops::FnOnce(i32) -> i32 cannot be statically determined
- --> $DIR/two-phase-nonrecv-autoref.rs:85:11
- |
-LL | f(f(10));
- | ^
-
-error[E0382]: use of moved value: `*f`
+error[E0382]: use of moved value: `f`
--> $DIR/two-phase-nonrecv-autoref.rs:85:11
|
+LL | fn twice_ten_oo(f: Box<FnOnce(i32) -> i32>) {
+ | - move occurs because `f` has type `std::boxed::Box<dyn std::ops::FnOnce(i32) -> i32>`, which does not implement the `Copy` trait
LL | f(f(10));
| - ^ value used here after move
| |
| value moved here
- |
- = note: move occurs because `*f` has type `dyn std::ops::FnOnce(i32) -> i32`, which does not implement the `Copy` trait
error[E0502]: cannot borrow `a` as immutable because it is also borrowed as mutable
- --> $DIR/two-phase-nonrecv-autoref.rs:129:27
+ --> $DIR/two-phase-nonrecv-autoref.rs:125:27
|
LL | double_access(&mut a, &a);
| ------------- ------ ^^ immutable borrow occurs here
@@ -60,7 +46,7 @@ LL | double_access(&mut a, &a);
| mutable borrow later used by call
error[E0502]: cannot borrow `i` as immutable because it is also borrowed as mutable
- --> $DIR/two-phase-nonrecv-autoref.rs:157:7
+ --> $DIR/two-phase-nonrecv-autoref.rs:153:7
|
LL | i[i[3]] = 4;
| --^----
@@ -70,7 +56,7 @@ LL | i[i[3]] = 4;
| mutable borrow later used here
error[E0502]: cannot borrow `i` as immutable because it is also borrowed as mutable
- --> $DIR/two-phase-nonrecv-autoref.rs:163:7
+ --> $DIR/two-phase-nonrecv-autoref.rs:159:7
|
LL | i[i[3]] = i[4];
| --^----
@@ -79,7 +65,7 @@ LL | i[i[3]] = i[4];
| mutable borrow occurs here
| mutable borrow later used here
-error: aborting due to 9 previous errors
+error: aborting due to 7 previous errors
-Some errors occurred: E0161, E0382, E0499, E0502.
-For more information about an error, try `rustc --explain E0161`.
+Some errors occurred: E0382, E0499, E0502.
+For more information about an error, try `rustc --explain E0382`.
diff --git a/src/test/ui/borrowck/two-phase-nonrecv-autoref.rs b/src/test/ui/borrowck/two-phase-nonrecv-autoref.rs
index 1a14cb90f38ef..1005da052970b 100644
--- a/src/test/ui/borrowck/two-phase-nonrecv-autoref.rs
+++ b/src/test/ui/borrowck/two-phase-nonrecv-autoref.rs
@@ -67,9 +67,9 @@ fn overloaded_call_traits() {
}
fn twice_ten_so<F: FnOnce(i32) -> i32>(f: Box<F>) {
f(f(10));
- //[nll]~^ ERROR use of moved value: `*f`
- //[g2p]~^^ ERROR use of moved value: `*f`
- //[ast]~^^^ ERROR use of moved value: `*f`
+ //[nll]~^ ERROR use of moved value: `f`
+ //[g2p]~^^ ERROR use of moved value: `f`
+ //[ast]~^^^ ERROR use of moved value: `f`
}
fn twice_ten_om(f: &mut FnMut(i32) -> i32) {
@@ -83,13 +83,9 @@ fn overloaded_call_traits() {
}
fn twice_ten_oo(f: Box<FnOnce(i32) -> i32>) {
f(f(10));
- //[nll]~^ ERROR cannot move a value of type
- //[nll]~^^ ERROR cannot move a value of type
- //[nll]~^^^ ERROR use of moved value: `*f`
- //[g2p]~^^^^ ERROR cannot move a value of type
- //[g2p]~^^^^^ ERROR cannot move a value of type
- //[g2p]~^^^^^^ ERROR use of moved value: `*f`
- //[ast]~^^^^^^^ ERROR use of moved value: `*f`
+ //[nll]~^ ERROR use of moved value: `f`
+ //[g2p]~^^ ERROR use of moved value: `f`
+ //[ast]~^^^ ERROR use of moved value: `f`
}
twice_ten_sm(&mut |x| x + 1);
diff --git a/src/test/ui/span/borrowck-call-is-borrow-issue-12224.nll.stderr b/src/test/ui/span/borrowck-call-is-borrow-issue-12224.nll.stderr
index 1a5ab7a7d56a0..4e2ab59f82245 100644
--- a/src/test/ui/span/borrowck-call-is-borrow-issue-12224.nll.stderr
+++ b/src/test/ui/span/borrowck-call-is-borrow-issue-12224.nll.stderr
@@ -18,7 +18,7 @@ LL | fn test2<F>(f: &F) where F: FnMut() {
LL | (*f)();
| ^^^^ `f` is a `&` reference, so the data it refers to cannot be borrowed as mutable
-error[E0596]: cannot borrow `*f.f` as mutable, as it is behind a `&` reference
+error[E0596]: cannot borrow `f.f` as mutable, as it is behind a `&` reference
--> $DIR/borrowck-call-is-borrow-issue-12224.rs:34:5
|
LL | fn test4(f: &Test) {
diff --git a/src/test/ui/span/borrowck-call-is-borrow-issue-12224.rs b/src/test/ui/span/borrowck-call-is-borrow-issue-12224.rs
index cfebd6f700359..f246f1118bf4e 100644
--- a/src/test/ui/span/borrowck-call-is-borrow-issue-12224.rs
+++ b/src/test/ui/span/borrowck-call-is-borrow-issue-12224.rs
@@ -32,7 +32,7 @@ fn test3<F>(f: &mut F) where F: FnMut() {
fn test4(f: &Test) {
f.f.call_mut(())
- //~^ ERROR: cannot borrow `Box` content `*f.f` of immutable binding as mutable
+ //~^ ERROR: cannot borrow field `f.f` of immutable binding as mutable
}
fn test5(f: &mut Test) {
diff --git a/src/test/ui/span/borrowck-call-is-borrow-issue-12224.stderr b/src/test/ui/span/borrowck-call-is-borrow-issue-12224.stderr
index 6c8f477e31062..a61ee8334afff 100644
--- a/src/test/ui/span/borrowck-call-is-borrow-issue-12224.stderr
+++ b/src/test/ui/span/borrowck-call-is-borrow-issue-12224.stderr
@@ -19,13 +19,13 @@ LL | fn test2<F>(f: &F) where F: FnMut() {
LL | (*f)();
| ^^^^ cannot borrow as mutable
-error[E0596]: cannot borrow `Box` content `*f.f` of immutable binding as mutable
+error[E0596]: cannot borrow field `f.f` of immutable binding as mutable
--> $DIR/borrowck-call-is-borrow-issue-12224.rs:34:5
|
LL | fn test4(f: &Test) {
| ----- use `&mut Test` here to make mutable
LL | f.f.call_mut(())
- | ^^^ cannot borrow as mutable
+ | ^^^ cannot mutably borrow field of immutable binding
error[E0504]: cannot move `f` into closure because it is borrowed
--> $DIR/borrowck-call-is-borrow-issue-12224.rs:56:13