How to differentiate between overloads when an argument is null

Question

This seems like something that I should have thought about before now, but it itn't. It also seems like there should be an existing way to do this.

The problem: Say I have a class with a couple of constructors

public class ModuleAction
{
    public ModuleAction(string url, string caption)
    { ... }

    public ModuleAction(string url, ModuleAction action)
    { ... }
}

And then elsewhere, I make a call to one of those constructors, but the second argument is null, it does not know which constructor to use

ModuleAction action = new ModuleAction("http://google.co.uk", null);

Is there any way of doing this? My current solution is to add an unused argument to one of the constructors, but that doesn't seem right.

My solution: (not pretty)

public class ModuleAction
{
    public ModuleAction(string url, string caption, bool unused)
    { ... }

    public ModuleAction(string url, ModuleAction action)
    { ... }
}

Answer 1

There are several options here.

The simple, direct solution is to cast the null to they type of the argument in the overload you wish to use:

ModuleAction action = new ModuleAction("http://google.co.uk", (string)null);

A better option would be to use a new constructor that has a single parameter and to chain it, using defaults:

public ModuleAction(string url) : this(url, "")