src/doc/unstable-book/src/language-features/unboxed-closures.md

   1 # `unboxed_closures`
   2
   3 The tracking issue for this feature is [#29625]
   4
   5 See Also: [`fn_traits`](../library-features/fn-traits.md)
   6
   7 [#29625]: https://github.com/rust-lang/rust/issues/29625
   8
   9 ----
  10
  11 The `unboxed_closures` feature allows you to write functions using the `"rust-call"` ABI,
  12 required for implementing the [`Fn*`] family of traits. `"rust-call"` functions must have
  13 exactly one (non self) argument, a tuple representing the argument list.
  14
  15 [`Fn*`]: ../../std/ops/trait.Fn.html
  16
  17 ```rust
  18 #![feature(unboxed_closures)]
  19
  20 extern "rust-call" fn add_args(args: (u32, u32)) -> u32 {
  21     args.0 + args.1
  22 }
  23
  24 fn main() {}
  25 ```