nameof expression (C# reference)
A nameof expression produces the name of a variable, type, or member as the string constant. A nameof expression is evaluated at compile time and has no effect at run time. When the operand is a type or a namespace, the produced name isn't fully qualified. The following example shows the use of a nameof expression:
Console.WriteLine(nameof(System.Collections.Generic)); // output: Generic
Console.WriteLine(nameof(List<int>)); // output: List
Console.WriteLine(nameof(List<int>.Count)); // output: Count
Console.WriteLine(nameof(List<int>.Add)); // output: Add
List<int> numbers = new List<int>() { 1, 2, 3 };
Console.WriteLine(nameof(numbers)); // output: numbers
Console.WriteLine(nameof(numbers.Count)); // output: Count
Console.WriteLine(nameof(numbers.Add)); // output: Add
You can use a nameof expression to make the argument-checking code more maintainable:
public string Name
{
get => name;
set => name = value ?? throw new ArgumentNullException(nameof(value), $"{nameof(Name)} cannot be null");
}
Beginning with C# 11, you can use a nameof expression with a method parameter inside an attribute on a method or its parameter. The following code shows how to do that for an attribute on a method, a local function, and the parameter of a lambda expression:
[ParameterString(nameof(msg))]
public static void Method(string msg)
{
[ParameterString(nameof(T))]
void LocalFunction<T>(T param) { }
var lambdaExpression = ([ParameterString(nameof(aNumber))] int aNumber) => aNumber.ToString();
}
A nameof expression with a parameter is useful when you use the nullable analysis attributes or the CallerArgumentExpression attribute.
When the operand is a verbatim identifier, the @ character isn't part of the name, as the following example shows:
var @new = 5;
Console.WriteLine(nameof(@new)); // output: new
C# language specification
For more information, see the Nameof expressions section of the C# language specification, and the C# 11 - Extended nameof scope feature specification.
