[Implement] subarray - #20

Can this maybe reuse the Uint8Array implementation, like in changetype<Buffer>(super.subarray(...))? Edit: Hmm, no, the id wouldn't match.

@dcodeIO We could reuse the parent class's version. All we have to do is change the rtId value.

let result = super.subarray(...);
let block = changetype<BLOCK>(changetype<usize>(result) - BLOCK_OFFSET); // whatever this is
block.rtId = idOf<Buffer>();
return result;

Best solution would just be to use the macro in the std lib but it's not exported.

Unless there are any problems with this implementation, can we pull this?

I will leave this as implemented for now because it's technically faster than:

let out = super.subarray(start, end);
changetype<BLOCK>(changetype<usize>(out) - BLOCK_OFFSET).rtId = idof<Buffer>();
return out;

How about use:

public subarray(begin: i32 = 0, end: i32 = 0x7fffffff): Buffer {
  return SUBARRAY<Buffer, u8>(this, begin, end);
}

And make SUBARRAY macro from typedarray.ts exportable.

Or even better move all typedarray's macros to new std/assembly/util/typedarray.ts file

@MaxGraey That would be nice, but I can't use the SUBARRAY function unless it's exported by the std library. Will have to wait until that changes.

Seems fine this way.

If AssemblyScript/assemblyscript#740 pulls, then I will refactor the current implementation to contain the utility functions.