Non-extensibility of Typed Arrays

Brendan Eich brendan at
Fri Aug 30 12:18:07 PDT 2013

David Herman wrote:
>> >  Typed Arrays are a different beast that already exist in the real world.  I don't see any need for consistency between Typed Arrays and struct types. Consistency between Typed Arrays and Array is more important.
> Mostly agreed, except I'd just refine that to say there's no need for consistency*in this dimension*. It would be a shame if typed arrays weren't generalized by the typed objects API in general, and I worked hard to make the pieces fit together. That nuance aside,

I think you are too kind :-|.

Allen, the point about typed arrays being different from structs because 
some implementations make the former extensible and the latter do not 
exist in any implementation yet is a just-so story, half of which is 
hypothetical! I could just as well argue from Firefox's non-extensible 
precedent if I wanted to.

The better argument is one that accounts for *why* structs are not 
extensible and how typed arrays differ, if they do differ, by design -- 
not based on implementation in some but not all browsers.

>   the fact that, in practice, arrays are patched with additional properties (in fact, IIRC the ES6 template strings API adds properties to arrays) suggests that non-extensibility would be a real incompatibility between arrays and typed arrays.

This only goes so far, since one could try to argue from objects to 
structs in the same way. What's the difference-in-kind reason? I can 
give answers but I'm looking for others' answers.

>   So I'm cool with making typed arrays -- but not structs -- extensible.

It's ok if we decide this, but let's have a not-just-so story beyond the 
array-like use-case one -- it's good but without something else, it 
could reason from objects to structs, but no one here wants extensible 
structs. (Right?)


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