c#: interpolated string to printout variable name and value

Question

Is there a shorter way to print out a variable name and its value in C#? What i do now is:

int myvar = 42;
Console.WritelLine($"{nameof(myvar)}={myvar}"); // or any other log function
//myvar=42

(I have been using Python a lot lately and really like pythons f"{myvar=}", which does exactly that.)

Thanks for your help

Answer 1

Yes-and-No.

No, you can't capture local variable names as simply as how Python does it.

...but it is possible by using a helper method with CallerArgumentExpression - this does require C# 10.0 and .NET 6+ - you also need to add [assembly: EnableCallerArgumentExpression] in your AssemblyInfo.cs.

Like so:

public static class MyExtensions
{
    public static String Dump<T>( this T value, [CallerArgumentExpression(nameof(value))] String? name = null )
    {
        String valueAsText;
        if( value == null )
        {
            valueAsText = "null";
        }
        else if( value is IEnumerable e ) // Can't use IEnumerable<T> (unless you use MethodInfo.MakeGenericMethod, which is overkill)
        {
            valueAsText = "{ " + e.Cast<Object?>().Select( i => i?.ToString() ).StringJoin() + " }";
        }
        else
        {
            valueAsText = '"' + value.ToString() + '"';
        }

        name = name ?? "(Unnamed expression)";

        return name + " := " + valueAsText;
    }

    public static String StringJoin( this IEnumerable<String?> collection, String separator = ", " )
    {
        return String.Join( separator: separator, collection.Select( s => s is null ? "null" : ( '"' + s + '"' ) ) );
    }
}

The Dump<T> method above is generic (over T) instead of using this Object? value to avoid unnecessary boxing of value when T is a value-type.

Used like so:

int myvar = 42;
Console.WriteLine( myvar.Dump() );
// myvar := "42"

Int32?[] arr = new[] { 1, 2, 3, (Int32?)null, 5 };
Console.WriteLine( arr.Dump2() );
// arr := { "1", "2", "3", null, "5" }

---

Screenshot proof:

(I had to name it Dump2 in the above screenshot because Dump is already defined by Linqpad).