refactor: Function for xrGetInstanceProcAddr calls

[curoviyxru]

No description provided.

[zmerp]

I would make a few changes. instead of a macro, use a normal function. Move the function at extra_extensions/mod.rs. For the function name, use a simple string parameter, and pass the xr prefix always, not worth trying to adding it back inside the function. Another thing, add inside the function .ok_or(sys::Result::ERROR_EXTENSION_NOT_PRESENT) and make it return xr::Result. then you just use the ? operator on the caller site.

[zmerp]

Looks good but I forgot to mention one last nit, to make it even more concise you could pass &Session directly instead of &Instance.

[zmerp]

Well almost good, but going full nitpicky, i say you should not use a reference here since later in this function you have to call to_owned(). Same for FaceTrackerPico::new(). Maybe I should have been more clear.

[curoviyxru]

Oh, so as I understand, I should avoid to_owned() and clone value beforehand instead if I need to move it?

[zmerp]

if you need to move the value, use a move parameter. if you need only references, then you use a reference parameter. it's better to always require to the caller any copies. This is for MultimodalMeta::new() and FaceTrackerPico::new(). I would make an exception maybe for functions called multiple times made to abstract common code AND they are not in a critical path, where I would use a reference regardless (like get_instance_proc, but actually this function doesn't need to own the Session so it doesn't matter)

[zmerp]

Looks good now, thanks!