Why aren't type constraints part of the method signature?

Question

UPDATE: As of C# 7.3, this should no longer be an issue. From the release notes:

When a method group contains some generic methods w

Answer 1

If T matches multiple constraints, you create an ambiguity that cannot be automatically resolved. For example you have one generic class with the constraint

where T : IFirst

and another with the constraint

where T : ISecond

You now want T to be a class that implements both IFirst and ISecond.

Concrete code example:

public interface IFirst
{
    void F();
}

public interface ISecond
{
    void S();
}

// Should the compiler pick this "overload"?
public class My where T : IFirst
{
}

// Or this one?
public class My where T : ISecond
{
}

public class Foo : IFirst, ISecond
{
    public void Bar()
    {
        My myFoo = new My();
    }

    public void F() { }
    public void S() { }
}