Object comprehension inside array comprehension - inconsistent compilation?

[Piotr Klibert]

Hello,

Recently I needed to rename some attributes on a couple of objects, which I got a list of. I did it like this (where f takes original name and returns new name):

new-obj-list = [ {[f(k), v] for k,v of obj} for obj in obj-list]

this didn't work - I got an array of arrays, where all the inner arrays had additional properties set to them. Compiled JS looks like this:

var newObjList, res$, i$, ref$, len$, obj, lresult$, k, v;
res$ = [];
for (i$ = 0, len$ = (ref$ = objList).length; i$ < len$; ++i$) {
  obj = ref$[i$];
  lresult$ = [];
  for (k in obj) {
    v = obj[k];
    lresult$[f(k)] = v;
  }
  res$.push(lresult$);
}
newObjList = res$;

It looks like `lresult$` is initialized with an empty Array instead of empty Object.

Normal nested loops are compiled to the same code:

new-obj-list = for obj in obj-list

    { [f(k), v] for k,v of obj }

var newObjList, res$, i$, ref$, len$, obj, lresult$, k, v;

res$ = [];

for (i$ = 0, len$ = (ref$ = objList).length; i$ < len$; ++i$) {

  obj = ref$[i$];

  lresult$ = [];

  for (k in obj) {

    v = obj[k];

    lresult$[f(k)] = v;

  }

  res$.push(lresult$);

}

newObjList = res$;

But when I do something - anything - with the inner obj comprehension it starts to work:

new-obj-list = for obj in obj-list

    z = { [f(k), v] for k,v of obj }

var newObjList, res$, i$, ref$, len$, obj, z, k, v;

res$ = [];

for (i$ = 0, len$ = (ref$ = objList).length; i$ < len$; ++i$) {

  obj = ref$[i$];

  res$.push(z = (fn$()));

}

newObjList = res$;

function fn$(){

  var ref$, results$ = {};

  for (k in ref$ = obj) {

    v = ref$[k];

    results$[f(k)] = v;

  }

  return results$;

}

Calling identity function on the inner obj comprehension works too.

Is this an expected behaviour?

[Isiah Meadows]

File a bug at https://github.com/gkz/LiveScript/issues.

Note that I've already found other issues with object literals, particularly where a condition gets duplicated in the output, which is bad.

[Piotr Klibert]

You do realize that this post is half a year old?

I since filed a bug, fixed it, created a PR and got it merged into LiveScript...