如何强制调用接口实现的方法？

Question

Considering: EqualityComparer.Default Property, its written in MSDN that:

The Default property checks whether type T implements the System.IEquatable interface and, if so, returns an EqualityComparer that uses that implementation. Otherwise, it returns an EqualityComparer that uses the overrides of Object.Equals and Object.GetHashCode provided by T.

My Understanding: As it will return EqualityComparer "object", So it should call overrides of Object.Equals and Object.GetHashCode provided by T(if it overrides or Object.Equals and Object.GetHashCode, otherwise). How could it call implemented method of IEquatable? Is it doing it forcibly? If yes, HOW? Correct me if i am wrong.

Here's the MSDN Link: http://msdn.microsoft.com/en-us/library/ms224763.aspx

Answer 1

Firstly, in a generic class as follows, actually the right method ( IEquatable<T> ) would be selected anyway:

    private class MyEqualityComparer<T> : IEqualityComparer<T> where T : IEquatable<T>
    {
        public bool Equals(T x, T y)
        {
            return x.Equals(y);
        }
        // Hashcode...
    }

Whereas if you cast y to object , the reference would be to object.Equals . This is just an overloaded method, and so that is resolved at compile time.