ArrayBuffer concat semantics

[bengl]

From #1:

1. A key goal is to provide an API for concatenation of two-or-more TypedArray instances in a single call that returns a new TypedArray and new backing ArrayBuffer.

What would the new backing ArrayBuffer look like? I'd suppose that TypedArrays referring to their entire backing buffer could simply concatenate those two buffers, but for TypedArrays referring to ranges smaller than their backing buffer, would the concatenated TypedArray have a buffer that it refers to entirely? I think that makes the most sense, and still gives implementors some room for implementing it lazily under-the-hood if desired.

[jasnell]

In that case, I would fully expect the resulting ArrayBuffer to refered to entirely. So, for instance,

const ab_1 = new ArrayBuffer(10);
const ab_2 = new ArrayBuffer(10);
const u8_1 = new Uint8Array(ab_1, 0, 5);
const u8_2 = new Uint8Array(ab_2, 5, 5);
const u8_3 = Uint8Array.concat([u8_1, u8_2]);

console.log(u8_3.buffer.byteLength);  // 10
console.log(u8_3.byteOffset);  // 0
console.log(u8_3.byteLength);  // 10

Additionally, when a Resizable ArrayBuffer is used as input, I think it makes the most sense fot the resulting ArrayBuffer to be a fixed sized based on the current size of the originals.

const ab_1 = new ArrayBuffer(10, { maxByteLength: 20 });
const ab_2 = new ArrayBuffer(10, { maxByteLength: 30 });
const u8_1 = new Uint8Array(ab_1, 0, 5);
const u8_2 = new Uint8Array(ab_2, 5, 5);
const u8_3 = Uint8Array.concat([u8_1, u8_2]);

// Not resizable
console.log(u8_3.buffer.byteLength);  // 10
console.log(u8_3.byteOffset);  // 0
console.log(u8_3.byteLength);  // 10
console.log(u8_3.buffer.resizable);  // false

As part of Immutable ArrayBuffer, I think we'll need to consider whether we need an option to concat-to-immutable or is transfering-to-immutable-after-concat good enough.

Really want to take the path of least surprise with this.

[ljharb]

If you concat arrays with a resizable buffer, the resulting array buffer should be resizable too.

[jasnell]

Resizable with what limit tho? Also, what if it's only one of the inputs that are resizable and the others aren't? I think it could be counter intuitive to users.