vulkano/TROUBLES.md

# Troubles encountered with Rust during the making of this library

- No way to store an object and its borrowing in the same struct. This is the reason why the whole API uses `Arc`s.

- Lack of plugins means that you have to use a build script to compile your shaders instead of inlining them directly where they are used.
  In addition to this, lots of existing macros would be much simpler to implement with plugins. The code generated by macros is currently
  inefficient because using the efficient way would make the code very difficult to read.

- Having a trait that defines which types can be put inside buffers is very annoying, as users have to implement it for every single struct
  they create. The best solution would be to use `impl BufferContent for ... {}`, but this syntax is still unstable.

- When `T` is unsized, there's no way to create a `*mut T` pointer from a `*mut c_void` and a size. This had to be implemented in a custom
  trait.

- The fact that is legal to implement `Deref` and make `deref()` return a different object every time means that it is dangerous to interface
  with a `Foo` through a `P where P: Deref<Foo>`. That `P` could return several different `Foo`s every time you deref it, and the implementation
  can't rely on the fact that the object will be the same every time.

- This library was designed with specialization in mind. There are several `is_compatible` trait methods that perform deep comparisons between
  layouts. With specialization available, these methods could be specialized as `true` for layouts that are known to always be compatible.

- https://github.com/rust-lang/rust/issues/29328

- "Source trait is private" errors when traits are declared in private modules but reexported publicly from a parent module. Not sure if that's
  a bug or a feature from the privacy system.

- Some trait implementations have an associated type that looks like `type T = (Arc<Foo>, Arc<Bar>);`. HKTs would allow this parameter to take
  references to the Arcs instead, and avoid having to clone them. This problem could by bypassed by making the code more ugly, but it's not worth
  it just to avoid cloning some Arcs.

- Visibility rules mean that you can't write `struct Error; pub mod foo { pub struct Foo; impl From<Error> for Foo { ... } }`. Rustc complains
  that `Error` is private an exported in `Foo`'s signature, even though that's in the author's opinion a totally legitimate usage.

- This repository contains the `vulkano-shaders` library, which generates Rust code that uses the `vulkano` library. If the API of `vulkano` gets
  a breaking change, there is no way to enforce or to check the fact that the user uses a correct combination of versions for `vulkano-shaders`
  and `vulkano`. Procedural macros declared in `vulkano` itself would solve this (https://github.com/rust-lang/rfcs/pull/1566).

- No way to set the alignment of a struct member, or to force the size of a struct to be a multiple of a certain size. Some parts of the Vulkan
  API enforce some limitations regarding the alignment, and the user currently has to manually add dummy padding fields.

- [No way to create dynamic-sized arrays on the stack](https://github.com/rust-lang/rfcs/issues/618). A lot of Vulkan functions require
  passing an array of small elements (small structs or integers). Building such an array with a `Vec` can be expensive, especially
  when most of the time the array only contains a single element. This is currently solved with the `SmallVec` type, but doing so wastes
  memory.