C# Define a tuple as type

Question

Is there a way in C# to define a custom type which holds a tuple? e.g.:

Type MyParams Tuple<string, string> ?

Motive: I have the following function in a parent class:

protected virtual IEnumerable<(string, string)> GetConfigs()

that will be overridden by each child class. I'm looking for a way to define that tuple as type to declare the return type as IEnumerable<Params> instead of duplicating the tuple.

Answer 1

• Create a record, which is a reference (C# 9+) or value type (C# 10+) which is immutable and behaves like a value type in both cases. A C# record is either a class or a struct having functionality added automatically by the compiler. See also Records (C# reference) and Use record types - C# tutorial | Microsoft Learn.
• Create a struct, which is a value type.
• Or declare:

  global using MyParams = System.ValueTuple<string, string>;
  

  Starting with C#12 you can create aliases for any type, i.e., also for ValueTuples:

  global using MyParams = (string key , string value);
  

This global using must precede any other using in the file. Versions prior to C# 12 do not allow creating aliases with the C# tuple syntax (string a, string b). Therefore, you will have to access the tuple elements with t.Item1, t.Item2 etc.

If you omit the global keyword (C# 10+), the scope of the directive is limited to the current file.

Now you can declare the method as

protected virtual IEnumerable<MyParams> GetConfigs()
{
   ...
}

Note; however, that this global using is only known in the current assembly!

Therefore, its use in a public API of a class library is limited.

It is still possible to access members of this library using this type, so.

Having this declaration in one assembly

global using MyParams = System.ValueTuple<string, string>;

namespace MyLibrary;

public class Class1
{
    public MyParams p = ("hello", "world");
}

You can write this in another assembly referencing the first one:

var obj = new MyLibrary.Class1();
Console.WriteLine(obj.p);

But a declaration like MyLibrary.MyParams p; is not possible in the other assembly.

Answer 2

What you're looking for is called alias using directive. However, according to the documentation you can define it with global scope starting from C# 10. Otherwise, you need to make an alias in every file when you want to use it.

using MyParams = System.Tuple<string, string>;

usage:

var foo = new MyParams("foo", "baz");