Add constructor pseudo-method

[dead-claudia]

Kind of like how classes have constructors to run on initialization, it'd be nice to add a way to run code "on implement", since interfaces/protocols might wish to have their own state (for example, for caching) and/or branding that's more specific than just "this implements me" or "this implements that".

Notes:

1. I'm not asking for arguments, which is something almost completely restricted to multiple-inheritance languages.
2. Such code would be run on Reflect.implement call or right after super on its result, in order of appearance in classes.
3. Any return value would be ignored.

[michaelficarra]

I'm thinking that a feature like this would be more appropriate for a decorator. I remember we've discussed notifying classes about extension, but I don't remember much about those discussions. @wycats and @allenwb would know more.

[michaelficarra]

Also, I'm generally opposed to the idea of a protocol being notified when it is implemented. I prefer explicit notification using existing mechanisms instead.

[dead-claudia]

I was thinking something along the lines of a parent "constructor", executed to initialize `this` for the protocol. Likewise, it doesn't run anything when used via `implements` in classes, much like how classes don't run anything when used via `extends`. Being notified of extension/implementation and potentially modifying classes I agree belongs in the realm of decorators, not protocols. Sorry if I wasn't clear enough initially.

…

On Tue, Sep 19, 2017, 22:01 Michael Ficarra ***@***.***> wrote: Also, I'm generally opposed to the idea of a protocol being notified when it is implemented. I prefer explicit notification using existing mechanisms instead. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#13 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AERrBFFCdfNcF0w8OmKyc8ijWAorcBGsks5skHISgaJpZM4PN_y-> .

[hax]

@michaelficarra Could you give a code example to show how to provide protocol own states via decorator?