How to get the name of a parameter?

Question

I have a parameter d. I want to use the name of the parameter in an error message:

void foo(string d)
{
    // this does not work
    string message string.Format("Parameter {0} is missing please verify inputs", d));
} 

How can I get the name of a parameter?

Answer 1

You can use nameof:

string nameOfD = nameof(d);

Note that this will not give the name of the variables used to call a method, it just works for the local variable. In this case, nameof will always return "d".

Answer 2

You can use Lambda expressions:

static void Main( string[] args ) {
    int A = 50, B = 30, C = 17;
    Print( () => A );
    Print( () => B );
    Print( () => C );
}

static void Print<T>( System.Linq.Expressions.Expression<Func<T>> input ) {
    System.Linq.Expressions.LambdaExpression lambda = (System.Linq.Expressions.LambdaExpression)input;
    System.Linq.Expressions.MemberExpression member = (System.Linq.Expressions.MemberExpression)lambda.Body;

    var result = input.Compile()();
    Console.WriteLine( "{0}: {1}", member.Member.Name, result );
}

Try this one.

Answer 3

You could use a concatenation of String.IsNullOrEmpty(variable)?nameof(variable):String.Empty. So you'd get

var str = String.Join(',', new List<String> 
  {
    String.IsNullOrEmpty(a)?nameof(a):String.Empty,
    String.IsNullOrEmpty(b)?nameof(b):String.Empty,
    String.IsNullOrEmpty(c)?nameof(c):String.Empty,
    String.IsNullOrEmpty(d)?nameof(d):String.Empty
});
string.Format("Parameter {0} is missing please verify inputs", str);