src/doc/unstable-book/src/language-features/infer-static-outlives-requirements.md

   1 # `infer_static_outlives_requirements`
   2
   3 The tracking issue for this feature is: [#54185]
   4
   5 [#54185]: https://github.com/rust-lang/rust/issues/54185
   6
   7 ------------------------
   8 The `infer_static_outlives_requirements` feature indicates that certain
   9 `'static` outlives requirements can be inferred by the compiler rather than
  10 stating them explicitly.
  11
  12 Note: It is an accompanying feature to `infer_outlives_requirements`,
  13 which must be enabled to infer outlives requirements.
  14
  15 For example, currently generic struct definitions that contain
  16 references, require where-clauses of the form T: 'static. By using
  17 this feature the outlives predicates will be inferred, although
  18 they may still be written explicitly.
  19
  20 ```rust,ignore (pseudo-Rust)
  21 struct Foo<U> where U: 'static { // <-- currently required
  22     bar: Bar<U>
  23 }
  24 struct Bar<T: 'static> {
  25     x: T,
  26 }
  27 ```
  28
  29
  30 ## Examples:
  31
  32 ```rust,ignore (pseudo-Rust)
  33 #![feature(infer_outlives_requirements)]
  34 #![feature(infer_static_outlives_requirements)]
  35
  36 #[rustc_outlives]
  37 // Implicitly infer U: 'static
  38 struct Foo<U> {
  39     bar: Bar<U>
  40 }
  41 struct Bar<T: 'static> {
  42     x: T,
  43 }
  44 ```