Optional assignment operator

[Darien Valentine]

True — though I’m not sure why concern for this case would merit new
syntax. Have you found that to be a common source of problems? Usually
setters are light / idempotent.

(Not opposed to the premise btw — just trying to hear more about what
problems it would solve, especially since syntactic solutions usually have
to be pretty high-value or else address something which can’t be  solved
any other way.)

On Wed, Jul 4, 2018 at 8:41 PM Jacob Pratt <jhprattdev at gmail.com> wrote:

> Sure, you'd be making an assignment no matter what in that case, which
> would unnecessarily trigger the setter, possibly causing side effects.
>
> ```
> const obj = {
>   get x() {
>     return _x;
>   },
>
>   set x(value) {
>     console.log('setter called');
>     _x = value;
>   },
>
>   demo(params = {}) {
>     ({ x: this.x = this.x } = params);
>   },
> };
>
> obj.demo({ x: 5 });
> obj.demo({ x: undefined });
> ```
>
> This will log twice, where it only needs to trigger it once.
>
> jhpratt
>
> On Wed, Jul 4, 2018 at 8:16 PM, Darien Valentine <valentinium at gmail.com>
> wrote:
>
>> > My thought was to have the following: this.foo ?= params?.foo; which
>> can be desugared to if (($ref = params?.foo) !== undefined) { this.foo =
>> $ref; }
>>
>> Are there any specific advantages to the new syntax you’re describing?
>> Initially, it appears to me like a less powerful form of an existing
>> syntactic feature — default initializers and binding patterns allow
>> expressing the same logic:
>>
>> ```
>> const obj = {
>>   demo(params={}) {
>>     ({ foo: this.foo=this.foo } = params);
>>
>>     console.log(
>>       `params was ${ JSON.stringify(params) }; ` +
>>       `this.foo is now ${ JSON.stringify(this.foo) }`
>>     );
>>   }
>> }
>>
>> obj.demo({ foo: 1 });
>> obj.demo({})
>> obj.demo({ foo: 2 });
>> obj.demo();
>> obj.demo({ foo: 3 });
>> obj.demo({});
>> ```
>>
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>>
>>
>
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