std.typecons: make RefCounted @safe

[wilzbach]

follow-up to #4685

[wilzbach]

I am not sure about this one. Is it safe to free memory from a pointer that we created and keep the reference too?

[schveiguy]

What we also need is a check to make sure RefCounted becomes @system when a @system ctor or dtor is on the target type.

Thanks, this looks pretty good!

[schveiguy]

Since we never expose a direct pointer to the ref counted payload, I think RefCounted can be perfectly safe.

Note, there is an existing issue for this: https://issues.dlang.org/show_bug.cgi?id=13983

[dnadlinger]

Unless I'm missing something, we cannot currently make RefCounted @safe in that way since refCountedPayload, i.e. the AliasThis, returns a reference (which is the entire point of RefCounted). You'd need to make that @system to be able to mark the destructor @safe, which of course isn't any better.

[jmdavis]

Unless I'm missing something, we cannot currently make RefCounted @safe in that way since refCountedPayload, i.e. the AliasThis, returns a reference (which is the entire point of RefCounted). You'd need to make that @System to be able to mark the destructor @safe, which of course isn't any better.

Yes, and that's a good part of why Walter is currently working on adding a ref-counting solution to the language - because while you can make ref-counting solution with a library, you can't make an @safe ref-counting solution with a library.

[schveiguy]

@klickverbot as long as you are in safe code, using the reference has to be while the ref-counted struct exists. You can't take the address of a ref in @safe code, so how is that unsafe?

[schveiguy]

Nevermind, I just realized that you can return a ref, so that would be bad. Yeah, we have to wait on this.

[nordlow]

Why is RefCounted not pure?

Because of malloc, free, etc? If so I believe it should:

https://github.com/dlang/phobos/pull/4832/files