C#•2y ago

✅ Interesting uses of yield return

I recently needed to generate an arbitrary number of unique random numbers, and after a little thinking I found I could get a really elegant solution by using yield return to generate an infinite stream of ints. This made me realise I basically never use this language feature and there's probably a lot of cool applications for it I'm missing. Any tricks/interesting patterns you've written with it?

16 Replies

BecquerelOP•2y ago

for anyone interested, what I did was this:

    private IEnumerable<int> GetRandom(int max)
    {
        while (true)
        {
            yield return Random.Shared.Next(max);
        }
    }

var randoms = GetRandom(someNumber)
.Distinct()
.Take(amount)
.ToList();

    private IEnumerable<int> GetRandom(int max)
    {
        while (true)
        {
            yield return Random.Shared.Next(max);
        }
    }

var randoms = GetRandom(someNumber)
.Distinct()
.Take(amount)
.ToList();

ero•2y ago

(basically just)

Enumerable.Range(0, amount)
.Select(_ => Random.Shared.Next(someNumber))
.Distinct()
.ToList();

Enumerable.Range(0, amount)
.Select(_ => Random.Shared.Next(someNumber))
.Distinct()
.ToList();

Kesa•2y ago

yield return is indeed very useful

ero•2y ago

I'd say it's rarely used in the way they're using it here

BecquerelOP•2y ago

damn, I should have thought of that!

Thinker•2y ago

What they're most useful for is probably returning collections of things where each item is potentially computationally intensive and where it's useful to let the caller decide how many items it needs. It's like a task in the sense that the caller can decide to interrupt the enumeration (and therefore execution of the method) at any time. (hell, Unity uses yield for its async stuff)

Anton•2y ago

this can give you fewer numbers than amount I suppose there's no built-in infinite range in linq

Cattywampus•2y ago

it's not true async btw coffeevee

ero•2y ago

Yeah I noticed as soon as I posted. Would this be a worthwhile proposal?

Anton•2y ago

what do you mean?

ero•2y ago

Propose an infinite range in Linq to dotnet/runtime

Anton•2y ago

I guess it's no different than introducing ISystemClock or similar helpers that you can code in 3 lines

canton7•2y ago

Why do you need an infinite range thing? If you keep asking OP's GetRandom for the next value, it will keep giving you one -- an infinite stream of random values. No need to generate an infinite range and then map each element to a random value, or something

BecquerelOP•2y ago

i will note one little discrepancy in my original code i'm curious about if the amount you .Take() is greater than max, the program will deadlock eventually i figured out this was because it's obviously impossible to have, say, 50 unique numbers less than 34 but i was surprised i didn't get an exception anywhere i don't know if there's an intelligent way to order the LINQ methods so that kind of subtle bug is more obvious think

canton7•2y ago

Hmm, I don't think so. The knowledge required to detect that problem is kinda spread out over the whole pipeline.

BecquerelOP•2y ago

RIP

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✅ Interesting uses of yield return