On Sun, Mar 29, 2015 at 10:49 PM, Allen Wirfs-Brock <al...@wirfs-brock.com> wrote:
> > > On Mar 29, 2015, at 11:51 PM, Caitlin Potter <caitpotte...@gmail.com> > wrote: > > > > ... > > > > Reflect.isConstructor(fn) -> true if Class constructor, generator, or > legacy (and non-builtin) function syntactic form > > Reflect.isCallable(fn) -> true for pretty much any function, except for > class constructors and a few builtins > > I’ve already seen another situation (node’s Buffer) where code could be > simplified by using a ES6 class definition but where that is prevented > because a class constructor throws when called. > > Just to clarify something. Class constructors actually are “callable”. > You can observe this by the fact that Proxy allows you to install an > “apply” handler (the reification of the [[[Call]] internal method) on a > class constructor. The the fact that an object can be [[Call]]’ed is > already reflected by the typeof operator. Class constructors throw when > called because at the last minute we choose to make their [[Call]] do an > explicit throw not because they aren’t callable. > > There is no intrinsic reason why we needed to mandate that class > constructors should throw when called. We even provided a simple and > straight forward way (new.target===undefined) that a ES constructor body > can use to determine whether it was called or new’ed. > > I think we should just drop that throws when called feature of class > constructors.. > (The restriction was added to future proof for the possibility of > inventing some other way to provide a class with distinct new/call > behavior. I don’t think we need nor can afford to wait for the invention of > a new mechanism which will inevitably be more complex than new.target, > which we already have.) > I don't think this is an accurate representation of the discussion we had. > > Allen > > > _______________________________________________ > es-discuss mailing list > es-discuss@mozilla.org > https://mail.mozilla.org/listinfo/es-discuss >
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