Regarding TypedArrays: - ToUint32 is definitely not sufficient for typed array indices because typed arrays are allowed to be longer that 2^32. - However the specified "clamping" of negative feels counter-intuitive to me: under the current spec "arr[-32] = 42" should assign 42 to arr[0]. This is not what current implementations of typed arrays, and this semantics seems confusing and dangerous.
Also, the systematic usage of ToPositiveInteger throughout the typed array/array buffer spec causes some counter-intuitive (or, at least, legacy-incompatible) behavior. For example, under the current spec "new Float32Array(-10)" silently allocates an array of length 0. Current typed array implementations throw in that case, and I think a case could be made that throwing here is better than allowing sloppy code. If people agree this is generally a thing to be avoided, I am happy to collect a systematic list of these issues and suggest fixes - but maybe I am missing something and that has some deep motivation? Kind regards, Dmitry On Tue, Apr 9, 2013 at 8:05 AM, Domenic Denicola < [email protected]> wrote: > I notice that operations accepting positive integers do various > somewhat-inconsistent things as of the latest ES6 spec: > > Various typed array things do `ToPositiveInteger`, a new operation as of > ES6: > > - `ArrayBuffer(length)` and `TypedArray(length)` > - Constructing a typed array, and `TypedArray.prototype.set`, coerce > both the passed object's `length` property and the numeric byte-offset > argument > - Most interestingly, `TypedArray.prototype.@@elementGet(index)` and > `@@elementSet(index, value)` do a `ToPositiveInteger` on `index`. So > `typedArray[-123] === typedArray[0]`, and `typedArray[-321] = 5` gives > `typedArray[0] === 5`. > > Whereas arrays use `ToUint32`, but sometimes throw `RangeError`s: > - Indices generally "work" if `ToString(ToUint32(index)) !== index`; > otherwise they're treated as ordinary properties. > - When getting a length from any array-like, you just do `ToUint32` on it. > - But when setting a length, you validate so that if `ToUint32(length) > !== length`, a `RangeError` is thrown. > > Finally, one lone place throws `RangeError`s after conversion: > > - `String.prototype.repeat(count)` throws if `ToInteger(count)` is > negative or infinite. > > --- > > I was curious if there were any interesting rationales driving these > decisions. (And I fully appreciate there might not be; it could just be > compatibility constraints.) Or, to put it another way, I was curious what > would be considered "idiomatic" JS, e.g. in the same way that the spec sets > a precedent of `ToString`-ing all string inputs to its functions. > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss >
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