Return array value

Feature Request

Overview

Not sure if this is a bug or not, I read through the docs and found no reference to this. Also tried looking through issues.

I can’t return an array. Correct me if i’m off here, but I think it’s because behind the scenes, walt is just grabbing the memory reference for the first element of the array. Similar to C if you print str (where str is an char[]), you’d just get the first char.

This is different from the issue about strings.

Impact

Large (if it doesn’t already exist).

Details

Here’s a dumb little example I tried:

const memory: Memory<{ initial: 1}>;

export function sortItems(array: i32[]): i32[] {
  let i: i32;
  let toReturn: i32[] = 0;
  for (i = 0; i < 5; i += 1) {
    toReturn[i] = i;
  }
  return toReturn;
}

I get Inconsistent return value. Expected i32[], received i32

Due Date

¯\(ツ)/¯ 7/20/18 if I missed something, I guess there is no due date.

I’m working on this for a hackday (which is only today), so either way, I’ll unfortunately have to ditch this project. I’m going to just use the C -> WASM compiler. However, I opened this issue because I’d like to experiment more in the future.

[njtrettel]

Okay, sorry for the long thread of questions. Now I’ve got the memory object imported from env in the walt code, and I have created a DataView with the buffer to read from. But whenever I try to do array operations in walt, I get an out of bounds error. I think I’m just missing something again.

~Apologies if this is documented. I searched for it and couldn’t find it here. The WebAssembly docs don’t help much in this case.~

EDIT: It sure is documented, I just missed the part that initial actual means the size 😄

@ballercat this is an awesome library, thanks for putting it together.

[ballercat]

Sure, all I mean is that it needs to be part of the imports to the WASM module. Per wasm spec, a Memory reference in a WebAssembly module is either declared or imported as a regular import with a memory type.

const memory = new WebAssembly.Memory({ initial: 1 });
makeSorter({
  env: {
    memory,
    log: console.log
  }
}).then(module => ...);

walt source, but really anything that compiles to wasm

import { memory: Memory<{ initial: 1 }> } from 'env';

MDN reference is a good source of info https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Memory