Attribute Macro nougat::gat

#[gat]

Entrypoint of the crate. Enables (lifetime) GATs on the annotated trait or impl block.

Example(s)

• #[macro_use]
  extern crate nougat;
  
  #[gat]
  trait LendingIterator {
      type Item<'next>
      where
          Self : 'next,
      ;
  
      fn next(&mut self) -> Option<Self::Item<'_>>;
  }
  
  struct WindowsMut<Slice, const SIZE: usize> {
      slice: Slice,
      start: usize,
  }
  
  #[gat]
  impl<Item, const SIZE: usize> LendingIterator for WindowsMut<&mut [Item], SIZE> {
      type Item<'next>
      where
          Self : 'next,
      =
          &'next mut [Item; SIZE]
      ;
  
      fn next(&mut self) -> Option<&mut [Item; SIZE]> {
          let to_yield =
              self.slice
                  .get_mut(self.start ..)?
                  .get_mut(.. SIZE)?
                  .try_into()
                  .expect("slice has the right SIZE")
          ;
          self.start += 1;
          Some(to_yield)
      }
  }

Remarks

• There is no need to use Gat! when inside a #[gat]-annotated item (since #[gat] will take care of automagically resolving the <Type as Trait>::Assoc<…> paths, as well as the Self::Assoc<…> ones), except when inside a macro! { … } invocation.

• Only lifetime GATs are supported, so no type-GATs:

  //! No HKTs or type families yet 😔
  #[macro_use]
  extern crate nougat;
  
  #[gat]
  trait Collection {
      type Of<T>;
  }
  
  enum Vec_ {}
  
  #[gat]
  impl Collection for Vec_ {
      type Of<T> = Vec<T>;
  }

• ⚠️ When use or pub useing a #[gat]-annotated trait, make sure to annotate such use “statement” with #[gat(AssocItem)].

  ⚠️ Otherwise it won’t be possible to implement that trait through the new path ⚠️

  For instance:

  extern crate nougat as nou;
  
  mod example {
      #[nou::gat]
      pub trait LendingIterator {
          type Item<'next>;
          // …
      }
  }
  
  // ⚠️ DO NOT FORGET TO ADD THIS ⚠️
  #[nou::gat(Item)] // 👈
  pub use example::LendingIterator;