How to modify an immutable array?

When using seamless-immutable, what is the recommended way of deriving new values from existing one (when map and merge aren’t enough)? Typically, immutable data structures (IDS) have functions that create new IDS derived from them, such as Immutable.js’ aList.push(1, 2) or Clojure’s updateIn, assocIn, dissoc, etc. In seamless-immutable all array/object mutating functions just throw an error so to create a new IDS I suppose I have to do something like

var newArray; var tmp = Immutable([1,2,3]).asMutable(); tmp.push(4); newArray = Immutable(tmp);

Is that correct? Thank you!

[rtfeldman]

Keep in mind that the function map accepts does receive index, so you can just do:

var indexToUpdate = 2, newVal = "THREE";

Immutable(["one", "two", "three", "four"]).map(function(val, index) {
  return (index === indexToUpdate) ? newVal : val;
});

Admittedly more verbose than mutableArray[indexToUpdate] = newVal, but in my experience this hasn’t come up all that often.

[bradwestfall]

oh, duh. Thanks