How to explicitly discard an out argument?

I'm making a call:

myResult = MakeMyCall(inputParams, out messages);

but I don't actually care about the messages. If it was an input parameter I didn't care about I'd just pass in a null. If it was the return I didn't care about I'd just leave it off.

Is there a way to do something similar with an out, or do I need to declare a variable that I will then ignore?

Solution 1:

Starting with C# 7.0, it is possible to avoid predeclaring out parameters as well as ignoring them.

public void PrintCoordinates(Point p)
{
    p.GetCoordinates(out int x, out int y);
    WriteLine($"({x}, {y})");
}

public void PrintXCoordinate(Point p)
{
    p.GetCoordinates(out int x, out _); // I only care about x
    WriteLine($"{x}");
}

Source: https://blogs.msdn.microsoft.com/dotnet/2017/03/09/new-features-in-c-7-0/

Solution 2:

You have to declare a variable which you will then ignore. This is most commonly the case with the TryParse (or TryWhatever) pattern, when it is used to test the validity of user input (e.g. can it be parsed as a number?) without caring about the actual parsed value.

You used the word "dispose" in the question, which I suspect was just unfortunate - but if the out parameter is of a type which implements IDisposable, you should certainly call Dispose unless the method documentation explicitly states that receiving the value doesn't confer ownership. I can't remember ever seeing a method with a disposable out parameter though, so I'm hoping this was just an unlucky choice of words.