0011-improved-cp-syntax.md

stage	start-date	release-date	release-versions	teams	prs	project-link	meta
discontinued	2014-09-30 00:00:00 UTC	2014-10-28 00:00:00 UTC	ember-source v1.8.0	framework	accepted #11		ember-issue emberjs/ember.js#9527

Summary

Improve computed property syntax

Motivation

Today, the setter variant of CP's is both confusing, and looks scary as sin. (Too many concepts must be taught and it is too easy to screw it up.)

Detailed design

today:

fullName: Ember.computed('firstName', 'lastName', function(key, value) {
  if (arguments.length > 1) {
    var names = value.split(' ');
    this.setProperties({
      firstName: names[0],
      lastName: names[1]
    });
    return value;
  }

  return this.get('firstName') + ' ' + this.get('lastName');
});

Tomorrow:

fullName: Ember.computed('firstName', 'lastName', {
  get: function(keyName) {
    return this.get('firstName') + ' ' + this.get('lastName');
  },

  set: function(keyName, fullName, oldValue) {
   var names = fullName.split(' ');

   this.setProperties({
     firstName: names[0],
     lastName: names[1]
   });

   return fullName;
  }
});

Notes:

• we should keep Ember.computed(fn); as shorthand for getter only
• get xor set variants would also be possible.
• { get() { } } is es6 syntax for { get: function() { } )

Migration

• 1.x support both, detect new behaviour by testing if the last arg is not null and typeof object
• 1.x+1 deprecate if last arg is a function and its arity is greater than 1

Drawbacks

N/A

Alternatives

N/A

Unresolved questions

None