Using yield makes the collection lazy. Let’s say you just need the first five items. Your way, I have to loop through the entire list to get the first five items. With yield, I only loop through the first five items.
It is something that F# supports with yield! for a whole collection vs yield for a single item. (That can be very useful in terms of tail recursion…) Unfortunately it’s not supported in C#. However, if you have several methods each returning an IEnumerable<ErrorInfo>, you can use Enumerable.Concat to make your code simpler: private static … Read more
Generators can’t be rewound. You have the following options: Run the generator function again, restarting the generation: y = FunctionWithYield() for x in y: print(x) y = FunctionWithYield() for x in y: print(x) Store the generator results in a data structure on memory or disk which you can iterate over again: y = list(FunctionWithYield()) for … Read more
Late answering, probably everybody knows about yield now, but some better documentation has come along. Adapting an example from “Javascript’s Future: Generators” by James Long for the official Harmony standard: function * foo(x) { while (true) { x = x * 2; yield x; } } “When you call foo, you get back a Generator … Read more
Inside a method that returns IEnumerable<T>, yield return has to return T, not an IEnumerable<T>. Replace yield return c.GetDeepControlsByType<T>(); with: foreach (var x in c.GetDeepControlsByType<T>()) { yield return x; }
I think the accepted answer is great, but it seems many people have failed to grasp some fundamental points. First, Scala’s for comprehensions are equivalent to Haskell’s do notation, and it is nothing more than a syntactic sugar for composition of multiple monadic operations. As this statement will most likely not help anyone who needs … Read more
It specifies that an iterator has come to an end. You can think of yield break as a return statement which does not return a value. For example, if you define a function as an iterator, the body of the function may look like this: for (int i = 0; i < 5; i++) { … Read more
Let’s get one thing out of the way first. The explanation that yield from g is equivalent to for v in g: yield v does not even begin to do justice to what yield from is all about. Because, let’s face it, if all yield from does is expand the for loop, then it does … Read more
Update Jan 2021: You can even do it in the Node REPL interactive using –experimental-repl-await flag $ node –experimental-repl-await > const delay = ms => new Promise(resolve => setTimeout(resolve, ms)) > await delay(1000) /// waiting 1 second. A new answer to an old question. Today ( Jan 2017 June 2019) it is much easier. You … Read more
The yield contextual keyword actually does quite a lot here. The function returns an object that implements the IEnumerable<object> interface. If a calling function starts foreaching over this object, the function is called again until it “yields”. This is syntactic sugar introduced in C# 2.0. In earlier versions you had to create your own IEnumerable … Read more