TypedArray: copyWithin/copyAllWithin are typed as returning array, and TypedArray.map can change the element type #9103

Found by a bug hunt over the 16 commits from eb087382 to cd641cbc.

copyWithin / copyAllWithin. These are typed as returning array<'a>. Per MDN, TypedArray.prototype.copyWithin returns the typed array it modified:

let v = Int32Array.fromArray([1, 2, 3])
let r = Int32Array.copyAllWithin(v, ~target=1)
let n = r->Array.push(5)

This compiles, then throws TypeError: r.push is not a function. The signatures are in Stdlib_TypedArray.res lines 128 and 145 (the generic module), and #9050 copied them into the Impl functor (lines 600 and 618), which all 11 typed-array modules include. Line 144 also has a duplicated @send @send.

TypedArray.map / mapWithIndex. The generic versions are typed (t<'a>, 'a => 'b) => t<'b> (lines 416 and 420). A typed array's map returns a typed array of the same kind and coerces each result to its element type:

let v: TypedArray.t<int> = %raw(`new Int32Array([1, 2, 3])`)
let s: TypedArray.t<string> = v->TypedArray.map(x => Int.toString(x) ++ "!")
Console.log(s->TypedArray.get(0))   // prints 0, typed option<string>

The Impl versions are typed T.elt => T.elt, which is correct. The generic copyAllWithin and map behave the same at b123b7c3.

🤖 Generated with Claude Code