How to allow a generic type parameter for a C# method to accept a null argument?

Question

private static Matcher EqualTo(T item)
{
    return new IsEqual(item);
}

How do I modify the above method definition suc

Answer 1

Consider the following method:

public bool IsNullString(T item) {
    return typeof(T) == typeof(string) && item == null;
}

Yes, this is a pathetically stupid method and using generics is pointless here, but you'll see the point in a moment.

Now consider

bool first = IsNullString(null);
bool second = IsNullString(null);

bool third = IsNullString(null);

In the first and second, the compiler can clearly distinguish the type of T (no inference is needed). In the third, how the compiler infer what T is? In particular, it can't distinguish between T == string and T == Foo, or any other type for that matter. Therefore, the compiler has to give you a compile-time error.

If you want to get around this, you either need to cast null

EqualTo((object)null);

or explicitly state the type

EqualTo