当用作字典中的键时，是否会覆盖结构导致装箱的GetHashCode？

Question

Normally if a struct implements an interface, assigning such struct to an interface variable causes boxing, eg:

interface IFoo {}

struct S : IFoo {}

S s = ...
IFoo f = s; // boxing here

However there are exceptions. It appears that implementing IEquatable<T> and using such struct in dictionary as a key, won't cause boxing. So the question is then, what if I just override GetHashCode without implementing IEquatable<T> ? Will it fall into some special case?

Answer 1

If you don't implement IEquatable<T> then the struct will be boxed when calling Equals . Equals is a virtual method and therefore requires a reference to obtain the associated method table.