How to create an overwriteable struct that is always const?

[David Zhang via Digitalmars-d-learn]

Say I have a struct `S`:

    struct S {
        /*const*/ char* pointer;
        ... other members ...
        this(/*const*/ char* p, ... others ...) {
            pointer = p;
            ...
        }
    }

What I want, is to be able to use `S` in other data structures 
with the following properties checked by the compiler:

 - The variable can be set
 - The variable can be read
 - The variable cannot be modified, only replaced

Is there a type-safe way to do this? If this were a class, I'd 
try std.typecons.Rebindable.

Thanks