On Wed, May 21, 2014 at 9:59 AM, Dmitry Lomov <[email protected]> wrote:
> I think it would be weird if some of them fail hard and some would behave > as if the length is zero. Consistency is always good. > Why "fail hard" is more desirable? > It is desirable because it allows for more efficient implementations in the common case. Quoting Allen Wirfs-Brock: Also note, that ignoring this new requirement, a Typed Array's length, > byteLength, and byteOffset are all constants and this fact is used in > specifying the behavior of the methods that operate upon them. If they can > change (even to 0) then this can occur on any operation that can trigger > side-effects. (For example, consider calling the callback function on > 'map' or similar methods). Do we really want to dynamically reconsider > changes to ;length' as opposed to simply letting throws to occur on access > to the neutered ArrayBuffer? [...] > In particular, I don't want to have to scatter length change checks > throughout thee algorithms in case one gets neutered as a side-effect of a > callback or a proxy mediated access. As a concrete example, when iterating over a typed array inside the `map()` implementation, it used to be possible to hoist the length of the array out of the loop, since it is a constant, and the loop can be unrolled if the length is known to be small. If the length of the array can change, the length needs to be re-checked on every iteration and unrolling typically won't happen. You can special-case this, since you know the only way the length can change is if the array is neutered -- but all this special casing adds up. It is cleaner (thus, in the absence of special-casing, faster) to use the existing exception mechanism to fail fast where necessary (for example, when you try to access the next element of an array which has been neutered). --scott
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