What is Scala's yield?

Question

I understand Ruby and Python\'s yield. What does Scala\'s yield do?

Answer 1

Unless you get a better answer from a Scala user (which I'm not), here's my understanding.

It only appears as part of an expression beginning with for, which states how to generate a new list from an existing list.

Something like:

var doubled = for (n <- original) yield n * 2

So there's one output item for each input (although I believe there's a way of dropping duplicates).

This is quite different from the "imperative continuations" enabled by yield in other languages, where it provides a way to generate a list of any length, from some imperative code with almost any structure.

(If you're familiar with C#, it's closer to LINQ's select operator than it is to yield return).