Nameof

This operator returns a string with a variable's name. It works at compile-time. It is a special compiler feature that simplifies some programs.

Though we can usually hard-code the names of variables in debugging output, nameof provides a more elegant solution. It can reduce duplication and thus errors arising from duplication.

Example

The nameof keyword returns a string containing the identifier of a variable. This is a compile-time feature. The compiler knows the names of variables, and it inserts them.

So We can use nameof even on local variables. We use it here to get an argument's name (size) and a local's name (animal).

using System;

class Program
{
    static void Test(int size)
    {
        // ... Write argument name with nameof.
        Console.WriteLine(nameof(size));
        Console.WriteLine(size);

        // ... Use nameof on a local variable.
        var animal = "cat";
        Console.WriteLine(nameof(animal));
    }

    static void Main()
    {
        // Call method.
        Test(100);
    }
}size
100
animal

Example 2

Consider this example, which writes the names and values of 2 local variables. We do not have the string literals "left" or "right" in the program.

Info We just reference the left and right variables by their names directly. So the compiler checks for spelling mistakes.

using System;

var left = 100;
var right = 200;

// Use nameof inside a string interpolation expression.
Console.WriteLine($"{nameof(left)} {left} {nameof(right)} {right}");
left 100 right 200

Summary

With nameof, we can use the C# compiler to check that the names of variables are correct when we write them to debug output. We do this by referencing the variable itself.