做接口变量的值类型和引用类型的语义？

Do interface variables have value-type or reference-type semantics?

接口是由类型实现的，这些类型或者是值类型或引用类型。很显然，无论是 INT 和字符串实施 IComparable的和 INT 是值类型，而字符串是引用类型。但对于这样的：

Interfaces are implemented by types, and those types are either value types or reference types. Obviously, both int and string implement IComparable, and int is a value type, and string is a reference type. But what about this:

IComparable x = 42;
IComparable y = "Hello, World!";

（我试图回答的问题是：presumably删除，因为它要求的接口是否被存储在堆栈或堆中的，正如大家应该都知道，这是更有建设性的思考价值之间的差异在它们的语义，而不是他们的执行方面引用类型。对于讨论，请参阅埃里克利珀的栈是一个实现细节。）

推荐答案

通常情况下，按照现有的答案，这是引用类型和需要拳;有一个例外，虽然（是不是总是存在？）。在一个通用的方法以其中，的约束，也可以是的两个的：

Usually, as per the existing answers, it is a reference-type and requires boxing; there is an exception though (isn't there always?). In a generic method with a where constraint, it can be both:

void Foo<T>(T obj) where T : ISomeInterface {
    obj.SomeMethod();
}

这是一个受限的操作，并没有盒装的即使的是一个值类型。这是通过constrained.相反，JIT进行操作的虚拟呼叫的引用类型，和静态调用的值类型。无拳。

This is a constrained operation, and is not boxed even if it is a value-type. This is achieved via constrained. Instead, the JIT performs the operation as virtual-call for reference-types, and static-call for value-types. No boxing.