Alternative syntax for <|

Brendan Eich brendan at mozilla.com
Thu Nov 17 13:27:21 PST 2011


On Nov 17, 2011, at 10:17 AM, Jason Orendorff wrote:

> On Thu, Nov 17, 2011 at 10:40 AM, David Herman <dherman at mozilla.com> wrote:
>> This isn't about scope, it's about at what point they're initialized. If you write:
>> 
>>    let x = new C();
>>    let C = class /* whatever */;
>> 
>> you won't get a scope error but a runtime initialization error. Whereas if you write:
>> 
>>    let x = new C();
>>    class C { ... }
>> 
>> it'll work fine.
>> 
>> I'm with Arv 150% on this.
> 
> I'm with Allen. If ES classes can contain any initialization code,

That's a big "if" right now.

The only way I see this happening is via static data property initialisers. The definition of static properties (of any kind) is not observable on the class or its prototype if |this| is verboten in initialiser expressions (for |this| read any keyword that allows access to the class constructor or prototype).

Of course, initialiser expressions could have side-effects in the heap (increment a global counter, e.g.). That's considered bad practice and I'm not sure worrying about it trumps the classes-as-sugar argument for hoisting: function declarations hoist today, people write constructors this way (most of the time), porting to classes which desugar this way suggests class declarations should hoist just as functions do to.

/be


> I think it should run in program order, interleaved with top-level
> statements. Anything else is just confusing.
> 
> Note that classdefs in Ruby and Python aren't hoisted, and nobody
> complains. In those languages classdefs very often contain procedural
> code, for many purposes.
> 
>    class Card   # Ruby
>        attr_accessor :rank, :suit    # macro-like
>    end
> 
>    class File:  # Python
>        size = property(get_size)    # create property descriptor
>        if os.name == 'posix':    # ifdef-like
>            ... posix-only methods ...
> 
> -j
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