How can a value type implement a ref type

Question

I came across a scenerio where a value type is implementing ref. type.

Just want to know how come is that possible ( what goes behind the scene ?)

A struct is a value type and interface a ref. type but a struct can implement interface without any error...

Any thoughts? Thanks in advance

Answer 1

Actually, it does it in two different ways at once.

Firstly, any value-type can be boxed into a reference-typed object instance. This box is invented by the runtime on demand and will implement the interface in the way you expect - i.e. the box will implement any interfaces the value-type implements.

However, the CLI also allows for a "constrained call". A constrained call turns a virtual call into a static call but only in exactly to the scenario where a value type implements an instance method by way of override or interface implementation (otherwise it is implemented by the JIT as a virtual call). In particular generics makes extensive use of constrained calls (the constrained opcode was added at the same time as generics, for exactly this reason).