C# 4.0 - How to Handle Optional String Parameters

Question

This code is not valid:

private void Foo(string optionalString = string.Empty)
{
   // do foo.
}

But this code is:

private void Foo(string optionalString = "")
{
   // do foo.
}

Why? Because string.Empty is a readonly field, not a constant, and defaults for optional parameters must be a compile-time constant.

So, onto my question... (well, concern)

This is what i've had to do:

private const string emptyString = "";

private void Foo(string optionalString = emptyString)
{
   // do foo.
   if (!string.IsNullOrEmpty(optionalString))
      // etc
}

How do you guys handle optional string parameters?

Why can they not make String.Empty a compile-time constant?

Answer 1

Ummm... what's wrong with string optionalParm = "" again? Why is that bad? Do you really think you need a symbolic constant for an empty string in this case? How about this then?

const int Zero = 0;

void SomeMethod(int optional = Zero) { }

Does that seem at all silly to you?

Answer 2

The best way to handle them is with:

private void Foo(string optionalString = "")
{
   // do foo.
}

So you can't use String.Empty. Everyone recognizes "", but if I found optionalString = nullString I wouldn't be sure what to think. If nothing else, name the thing emptyString--it's not null!

Answer 3

I'm answering this question.

Why can they not make String.Empty a compile-time constant?

Here is the disassemble code via Reflector of String.cs in mscorlib.dll

public static readonly Empty;
static String()
{
    Empty = "";
    WhitespaceChars = new char[] { 
        '\t', '\n', '\v', '\f', '\r', ' ', '\x0085', '\x00a0', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', 
        ' ', ' ', ' ', ' ', '​', '\u2028', '\u2029', '　', ''
     };
}

So in windows platform, string.Empty is exactly "". But do you know, Martian have a different definition for Empty and WhitespaceChars in their OS.

Answer 4

if you don't like "" value you can use default(string).
I played with it and it is allowed.

private static void foo(string param = default(string)) {
    if (!string.IsNullOrEmpty(param)) // or param != default(string)
        Console.WriteLine(param);
}