Question

One of the common programming best practices is "define variables as close to where they are used as possible".

I use structs frequently to create code thats almost self documenting in places. However, C# forces me to define the struct outside the method. This breaks the aforementioned best practice – its basically creating an unwanted global variable type for the entire class.

Is it possible to define a local struct inside a method, just like a local variable, and if not, could you give me a window into the reasons the C# designers decided to prevent this?

Use Case

I’m converting part of a spreadsheet into C# code. I’d like to use local structs within the method to store temporary information in an organized manner, without having to resort to hundreds of separate variables that are global in scope.

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Update 2016-August: C# 7.0 may have this feature!

As of 2016-Aug, apparently, this will be a feature in C# 7.0.

So the C# compiler team agreed – wow!

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Update 2020-July: Now supported by C# and C++

C++ has always fully supported this. And it’s fantastic.

C# 7.0 now has value tuples for a lightweight data structure with named fields. See answer from Ghost4Man.

Answer 1

I believe it’s not permitted to define named types within a method. As to why, I’ll have to speculate. If a type is not going to be used outside, then its existence probably cannot be justified.

You can however define anonymous type variables within a method. It will somewhat resembles structures. A compromise.

public void SomeMethod ()
{
    var anonymousTypeVar = new { x = 5, y = 10 };
}