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C# 11–The scoped keyword

While browsing through the source code of the .NET framework(what else would you do with some free time?) I noticed the usage of the scoped keyword:

This triggered my interest as I didn't know that this keyword existed. Time to find out what it does...

To explain what this keyword does, I have to talk first about ref struct. C# 8 introduced ref struct where it was used to implement the Span type. A ref struct guarantees that an instance of the type is allocated on the stack and can’t escape to the managed heap. To guarantee this, strict scoping rules are enforced by the compiler.

More about ref structure types here: ref struct types - C# reference | Microsoft Learn

When you pass references to methods on a ref struct, the compiler ensures that the variables you refer to don't go out of scope before the struct itself. Otherwise, the ref struct might refer to out-of-scope variables:

The code above results in a compiler error:

The fix is to introduce the scoped keyword. Now the compiler will allow to pass these variables and it will treat the argument with the same scope as a local variable in the method.

Hope that helps…

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