Can I create a c# method which might return different types?

Questions & Answers
1

I want to do something along the lines of this:

public class Foo {

	private int barI;
	private float barF;
	
	public <what would go here?> Get( bool isInt ) {
		if (isInt) return barI;
		else return barF;
	}
		
}

… where a single method can return an int or a float depending on circumstances. But I suspect it’s impossible… or is it?

3

Unfortunately because numbers don’t have a consistent inheritence hierarchy this is difficult to do in the Mono/.Net platform. This is a post on SO about this and it’s a known ‘feature’. Oddly enough C# does not have a constraint that says void TThing GetThing(bool b) where TThing : some number. A pretty gaping hole in their generics IMHO. numbers have some common ancestry (the Single class and all it’s interfaces) but this hierarchy cannot be used as a constraint and even if it could there are no operators on it anyway that you would typically care about. All the operators are defined elsewhere.

4

You can have the method return object like so:

private int barI;
private float barF;

private object Get(bool isInt)
{
    if (isInt)
        return barI;
    else return barF;
}

But you’d have to cast the returned object to the correct type when you call the method:

int integer = (int)Get(true);
float single = (float)Get(false);

If you get that mixed up and try to cast the returned object to something it isn’t, you’re in trouble.

2

I guess you could return a hashtable, and check the existing keys in it to see what was returned.

5

You can create a constraint that accepts only float and int, but unfortunately it can’t perform the cast to T in this case. Generics work different than C++ templates.

public class Foo
{
    private int barI;
    private float barF;

    public T Get<T>() where T : float,int
    {
        T tmp;
        if (tmp is int) 
            return (T)barI;  // WON'T WORK !
        else 
            return (T)barF;  // WON'T WORK !
    }
}