On Wednesday, 4 March 2020 at 12:03:48 UTC, Gregor Mückl wrote:
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.
You can use move maybe? :
https://dlang.org/library/std/algorithm/mutation/move.html
So
this.f = f.move;
But you should be aware that it could cause problems when f has
pointers to its internals. I.e. if Foo had a pointer to it's own
member then the value of of that pointer to me "copied" over to
this.f, but the address of the member in this.f is different that
the original f's member address.
