Defer keyword

[simon-curtis]

I’ve seen previous discussions about the defer keyword, but they mainly focused on its use for disposal scenarios. One comment even mentioned that they couldn’t find another practical use case.

However, I recently encountered a case where defer would be particularly useful—when working with ArrayPool. Consider the following example:

var bytes = ArrayPool<int>.Shared.Rent(1024);
defer ArrayPool<int>.Shared.Return(bytes);

// Use bytes until the end of the scope

This approach improves readability by reducing nesting, similar to how C# has evolved with features like top-level statements and primary constructors. While defer in C# would just be syntactic sugar, it helps make resource management cleaner without adding significant complexity.

I could easily see this being the preferred syntax for almost any occasion you find yourself reaching for a finallycase.

Of course, misuse could be a concern—just like accidentally using a using statement on a singleton or pooled DbContext. However, developers in other languages appreciate this feature greatly, and given that it would be a lightweight compiler addition, I believe it’s worth considering for C#.

Would love to hear people's thoughts on this.

[HaloFour]

Here's the existing discussion on a defer statement: #513

IMO, returning a leased resource falls under resource disposal. It's not difficult to create an adapter to ArrayPool<T> that would allow you to lease a buffer in a using block via extension method.

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