true private members & symbols ?

[ichiriac]

Hi,

Is there any reason you don't use symbols for private properties on classes ? I'm really interested on what you have done with typescript and try something similar so I'm maybe missing something.

Best Regards,
Ioan

[ichiriac]

BTW, I've read all thread on Stackoverflow http://stackoverflow.com/questions/12713659/typescript-private-members and Codeplex https://typescript.codeplex.com/discussions/397651 but they don't speak about symbols so maybe they are too old as symbols were introduced lately.

[DanielRosenwasser]

We once got a PR from @Arnavion (see #684), however, the emit has some issues.

At the time, @NoelAbrahams noted:

• Class instantiation is about 60% slower when using symbols.
• Property and method access is about 90% slower when using symbols.
• The codegen when using symbols is not minification-friendly; even advanced optimisation will not minify string literals such as __symbol("_property_p");

Things might have changed in terms of speed, but at this point I'd rather we didn't change our private emit until we see the direction ECMAScript takes with the private slots proposal. In fact, I don't think our public, private, or protected modifiers should have any sort of impact on emit.

[ichiriac]

Hi @DanielRosenwasser,

Many thanks, it's very helpfull all these links. Finger crossed for private slots, anyway they already reserved the private keyword http://www.ecma-international.org/ecma-262/6.0/#sec-future-reserved-words

[Yogu]

Class instantiation is about 60% slower when using symbols.
Property and method access is about 90% slower when using symbols.

Seems no longer to be true, property access is 2% slower and instanciation performance is equal for me (Chrome 56). By the private slot proposal, do you mean the tc39 proposal-private-fields?

[ichiriac]

Sadly, symbols will not be a guarantee to make things fully private : https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/getOwnPropertySymbols

Not tested yet, but seems obviously slow, is to use : https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap