Saturday 11 April 2020

Using yield return in CSharp

I was not very sure on the use of yield return in C#, until I read completely about it in very simple manner. I will try my best to share all I learned in as simple words I can.

I know it’s a very old thing and many people online use it, but I believe there, still, are many developers like me who are avoiding it because all the books and articles explain it in very few words at very high level view.

So, let us just start with a simple premise, we need a function to return list of numbers from a very large sequence. An example can be to return the list of first 100 even numbers, assume that later on in the program we are processing our list of 100 even numbers. In your case it can be to pull the record of customers from database on certain condition.

Well there are many efficient ways to write the same program, I intentionally chose this, as this post is about keeping it simple.

If you keep the input as 100, there is no major memory allocation, but if the input is changed to 1million or more, the memory allocated for execution of the program increases drastically. Same can be checked using diagnostic tools in visual studio.

We live in the world where memory cost is always ignored against CPU, but that should not be our reason to fill the stack when we can do better.

yield return is a solution. I wrote the same program as above, the only difference is the return type. Instead of returning the List we are here returning IEnumberable.

Don’t even think of counting the elements in the sequence. This is IEnumerable, not IQueryable. IEnumberable<T> exist in System.Collections.Generic.
IQueryable exists in System.Linq. This article talks about the difference in detail.
You can find the complete program on github.

I hope this was easy. Please share your thoughts in the comments below.

1 comment:

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