Question

If I’m calling a method that uses a out or ref parameter why do you need to mark the parameters with out or ref when calling the method? i.e.

DateTime.TryParse(myDate, out dateLogged)

I had thought this was something to reduce ambiguity when operator overloading but if I create two methods like so:

void DoStuff(int x, out int y)
{
    y = x + 1;
}

void DoStuff(int x, ref int y)
{
    y = x + 1;
}

Then Visual Studio reports “Cannot define overloaded method ‘DoStuff’ because it differs from another method only on ref and out”, so I couldn’t do that anyway.

EDIT:

After a bit more research it seems that I would need to specify out or ref when calling a method if it there were two overloaded methods declared like this:

    void DoStuff(int x, out int y)

    void DoStuff(int x, int y)

Answer 1

It’s there so that you’re explicitly consenting to the possibility that the method you’re calling could modify the value of the variable itself. This is a C# language requirement; other languages like VB.NET do not require you to decorate the actual method call, just the method signature.