Feature-Request: allow to iterate over WeakSet / WeakMap

[Isiah Meadows]

Could you explain a real world use case for this? I recall some that it
would've simplified some, but the best implementation often didn't even
require iteration, but just changing the data layout altogether.

On Wed, Jul 13, 2016, 08:13 Michael Kriegel <michael.kriegel at actifsource.com>
wrote:

> Hi everyone,
>
> not sure, whether this is the right place for discussing a feature
> request - and how to find out, whether this was already
> proposed/discussed before and with which result... My google search did
> not bring up anything about it.
>
> On my opinion it should be made possible to iterate over all elements in
> a WeakSet & WeakMap. I already found many cases, in which I'd like to
> have used the neat feature of "garbage collect the object, if it is not
> referred to by others anymore", but with the necessity to know, which
> objects are in the set (not only, if a given object is). An example:
>
> Registering callbacks to objects:
>
> class Foo {
>    onBla(Handler) {
>      this.BlaSuperWeakMap.push(Handler);
>    }
>
>    someOtherMethod() {
>      for (let X in this.BlaSuperWeakMap) {
>        X();
>      }
>    }
>
>    constructor() {
>      this.BlaSuperWeakMap = new SuperWeakMap();
>    }
> }
>
> const MyFoo = new Foo();
> {
>    let MyHandler1 = function(){
>      console.log('MyHandler1 called');
>    };
>    MyFoo.onBla(MyHandler1);
>    console.log('Invokation1:');
>    MyFoo.someOtherMethod();
> }
> let MyHandler2 = function(){
>    console.log('MyHandler2 called');
> };
> MyFoo.onBla(MyHandler2);
> MyFoo.onBla(function(){
>    console.log('MyHandler3 called');
> });
> console.log('Invokation2:');
> MyFoo.someOtherMethod();
> MyHandler2 = undefined;
> console.log('Invokation3:');
> MyFoo.someOtherMethod();
>
> Expected result:
>    Invokation1:
>    MyHandler1 called
>    Invokation2:
>    MyHandler2 called
>    Invokation3:
>
> Basically the example is: Invoke the callback of all objects which still
> "exist" (in the meaning of having "non-weak" references towards them).
>
> I know this may have some caveats. It would be necessary to check the
> reference count of the object in the SuperWeakSet, because the object
> may have no "non-weak" references left but still was not yet garbage
> collected. I do not know, whether current ECMAScript-Implementations and
> their garbage collecting solutions could handle this easily - basically
> it is the same decision, which the garbage collector would make: If an
> object can be disposed, because it has no non-Weak references pointing
> to it, the object is by definition not in the WeakSet anymore. And
> implementations could in that case even give a hint to the garbage
> collector, which may improve performance of applications, which use the
> SuperWeakSet alot.
>
> Greetings, Michael
>
>
>
>
>
>
>
>
>
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