Member with the same signature already defined with different type constraints

Question

I have run across an issue with overloading methods that have different constraints that seems exclusive. That is my example:

public class A
{
    public void Do<T>() where T : class
    {

    }

    public void Do<T>() where T : struct 
    {

    }
}

And this does not compile with the following error "Member with the same signature already defined". Is it possible to satisfy both conditions at once or it's just the limitation of the C# compiler?

Answer 1

It's not a limitation of the compiler - it's a limitation of the language (and quite possibly the CLR as well; I'm not sure).

Fundamentally those are clashing overloads - it's like trying to overload by return type. It's not supported.

It is possible to declare methods such that these calls all compile to invocations of different methods:

a.Do<int>();
a.Do<string>();
a.Do<int?>();

... but it always involves optional parameters and/or parameter arrays, and it's horrible.

Also note that although you can't overload by generic constraints, you can overload by the generic "arity" (the number of type parameters):

public void Foo() {}
public void Foo<T>() {}
public void Foo<T1, T2>() {}

Answer 2

You cannot overload a method by varing the generic parameter containts. For a valid method overload you have to have different input parameters to the method.

Answer 3

Both methods should have the following name when compiled:

A.Do``1

As the count of generic parameters goes into the name of the method or class.

Not sure what your situation is but you may need to make use of reflection to call those methods:

public class A
{
    public void Do<T>()
    {
        if(typeof(T).IsValueType){
            // nasty reflection to call DoValueType
        }
        else {
            // nasty reflection to call DoReferenceType
        }
    }
    private void DoReferenceType<T>() where T : class {

    }
    private void DoValueType<T>() where T : struct {

    }
}