add section in book

rust-lang · bors · Jul 28, 2018 · Jul 27, 2018 · Jul 27, 2018 · Jul 27, 2018
commit 130e3ab31b28c9839e2f04c98c4b62c6f1c215a3
diff --git a/src/doc/unstable-book/src/language-features/infer-static-outlives-requirements.md b/src/doc/unstable-book/src/language-features/infer-static-outlives-requirements.md
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+# `infer_static_outlives_requirements`
+
+The tracking issue for this feature is: [#44493]
+
+[#44493]: https://github.com/rust-lang/rust/issues/44493
+
+------------------------
+The `infer_static_outlives_requirements` feature indicates that certain
+`'static` outlives requirements can be infered by the compiler rather than
+stating them explicitly.
+
+Note: It is an accompanying feature to `infer_outlives_requirements`,
+which must be enabled to infer outlives requirements.
+
+For example, currently generic struct definitions that contain
+references, require where-clauses of the form T: 'static. By using
+this feature the outlives predicates will be infered, although
+they may still be written explicitly.
+
+```rust,ignore (pseudo-Rust)
+struct Foo<U> where U: 'static { // <-- currently required
+    bar: Bar<U>
+}
+struct Bar<T: 'static> {
+    x: T,
+}
+```
+
+
+## Examples:
+
+```rust,ignore (pseudo-Rust)
+#![feature(infer_outlives_requirements)]
+#![feature(infer_static_outlives_requirements)]
+
+#[rustc_outlives]
+// Implicitly infer U: 'static
+struct Foo<U> {
+    bar: Bar<U>
+}
+struct Bar<T: 'static> {
+    x: T,
+}
+```
+