Why do T and *T have different method sets?
From the Go Spec: The method set of any other named type T consists of all methods with receiver type T. The method set of the corresponding pointer type *T is the set of all methods with receiver *T or T (that is, it also contains the method set of T). If an interface value contains a pointer *T, a method call can obtain a value by dereferencing the pointer, but if an interface value contains a value T, there is no useful way for a method call to obtain a pointer.
