AshMemoryDevice could avoid unsafe code during construction

[i509VCB]

At the moment the following is done:

    #[repr(transparent)]
    pub struct AshMemoryDevice {
        device: Device,
    }
    
    impl AshMemoryDevice {
        pub fn wrap(device: &Device) -> &Self {
            unsafe {
                // Safe because `Self` is `repr(transparent)`
                // with only field being `DeviceLoader`.
                &*(device as *const Device as *const Self)
            }
        }
    }

This works but requires what I feel is unnecessary unsafe code.

I imagine we could change AshMemoryDevice to the following if we use a lifetime:

pub struct AshMemoryDevice<'a> {
    device: &'a Device,
}

impl AshMemoryDevice<'_> {
    pub fn wrap(device: &Device) -> Self {
        Self { device }
    }
}

[zakarumych]

I'm wouldn't like passing multilevel references everywhere. So then all API must accept device by value and require Copy. Not sure API would look better that way.

[nerditation]

if I understand it correctly, the reason there's the wrapper type AshMemoryDevice is due to the orphan rule; the wrapper type would be totally unneccessary if the "backend implementations" (e.g. gpu-alloc-ash) are not separate crates but instead sub-modules of the same crate, and selectable by cargo feature flags. that way, you could simply

impl crate::MemoryDevice<vk::DeviceMemory> for ash::Device{
//...
}

and use the ash::Device directly for alloc, dealloc, cleanup, etc

so I wonder? is there any plan for furture work toward this direction?

---

PS: to be honest, I feel it a little inconvenient having to write AshMemoryDevice::wrap(&device) a lot.

with the current implementations, I would suggest to make it more ergonomic to use , for instance, if we change the signature to:

pub unsafe fn cleanup<MD: MemoryDevice<M>>(&mut self, device: impl AsRef<MD>);

and besides AshMemoryDevice::wrap, we also add impl AsRef<AshMemoryDevice> for ash::Device {...}, then we can call the function like this:

// just a plain `ash::Device`, no need to manually wrap it
let device: ash::Device;
//...
// need this in scope so the so type inference could resolve
// or, explictly specify the type argument without import into scope
use gpu_alloc_ash::AshMemoryDevice
allocator.cleanup(&device);
allocator.cleanup::<gpu_alloc_ash::AshMemoryDevice>(&device);

[zakarumych]

The reason to have separate crates is flexibility in version updates. Crate for each backend is updated with backend's nee version. And main crate can be updated separately from them.

[zakarumych]

API ergonomics suggestions and PRs are welcome

[nerditation]

The reason to have separate crates is flexibility in version updates.

right, that makes perfect sense

API ergonomics suggestions and PRs are welcome

ok, I think I can make a PR. it should be trivial to impelement, and I believe it should not break old code.

[nerditation]

#65 is created.