Muhammad Waseem (@mwaseemzakir) on X

The post explains that yield is used for custom stateful iteration over .NET collections. It contrasts building a full list and returning it with letting the caller consume values during iteration, and says yield basically returns an IEnumerable. It also notes that C# 8 adds IAsyncEnumerable and that yield works lazily, so values are not retrieved until the collection is iterated or materialized with ToList().

Reading notes

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• yield return and yield break are presented as the key forms of the keyword.
• The example focuses on checking even numbers between 1 and 1000.
• One approach stores all results in a list before returning them.
• Another approach keeps iterating and reports numbers to the caller as it goes.
• yield is described as useful for that second approach.
• Methods with ref, in, or out parameters are said not to allow yield.
• Lambda expressions and anonymous methods are said not to contain yield.
• The post says the sequence is only retrieved when iterated with a for loop or when ToList() is used.