Safely wrapping an uncopyable struct to implement an interface

[Gregor Mückl]

Hi!

I've just created a situation in my code that is summarized by 
the following example. I don't know how to solve it with @safe 
code.

A third party library provides a struct that is not copyable:

// provided by third party
struct Foo {
     @disable this() @safe;
     @disable this(ref return scope Foo other) @safe;

     void magic() @safe;
}

What I want to do is to provide a safe wrapper around it that 
adapts to another interface:

// intended common interface
interface IWrapper {
     void bar() @safe;
}

Now, the obvious way to wrap this fails:

class FooWrapper : IWrapper {
     Foo f;

     this(Foo f) @safe {
         this.f = f; // this fails because it would be a copy
     }

     override void bar() @safe
     {
         f.magic();
     }
}

If Foo were a class, f would be a reference and everything would 
be fine. But f is a struct that can't be copied and taking a 
pointer to f makes FooWrapper obviously unsafe. How could I solve 
this?

I've come up with a workaround for my actual use case that 
doesn't need to use the uncopyable struct this way. But I'm 
curious if I'm missing something regarding references to structs.