Non-extensibility of Typed Arrays

Oliver Hunt oliver at
Fri Aug 30 10:18:48 PDT 2013

On Aug 30, 2013, at 10:13 AM, David Herman <dherman at> wrote:

> On Aug 30, 2013, at 9:39 AM, Allen Wirfs-Brock <allen at> wrote:
>> I think the right-way to think about structs is as an record structure with no properties fixed behavior provided by a "wrapper".  Very similar to the ES primitives except that structs can be mutable.  The way to associate properties with structs is to encapsulate them in an object, preferably via a class definition. If we go that route we can reach the point where ES classes have fixed-shape internal state defined as-if by a struct.
> I might give a slightly different angle on this, and describe structs as objects with a fixed template for their own properties. They are still objects, they still inherit from prototypes. But they have a predefined set of own properties.
>> 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, 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. So I'm cool with making typed arrays -- but not structs -- extensible.

I think of TypedArrays as being Arrays of structs with a fixed type/shape - the Array itself is a regular object with regular property characteristics, whereas the individual elements are all value types .

For example, say i have a struct type S, and make a regular Array filled with S.  Aside from the poor performance, this is now essentially what a typed array of structs is.  What is the reason for making the fast version of an array of structs lose the features of a regular array filled with structs?


> Dave
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