-An underscore `_` character has been used as the identifier for a lifetime.
+`'_` lifetime name or `&T` without an explicit lifetime name has been used
+on illegal place.
Erroneous code example:
```compile_fail,E0106,E0637
-fn longest<'_>(str1: &'_ str, str2: &'_ str) -> &'_ str {
- //^^ `'_` is a reserved lifetime name
+fn underscore_lifetime<'_>(str1: &'_ str, str2: &'_ str) -> &'_ str {
+ //^^ `'_` is a reserved lifetime name
if str1.len() > str2.len() {
str1
} else {
str2
}
}
+
+fn and_without_explicit_lifetime<T>()
+where
+ T: Into<&u32>,
+ //^ `&` without an explicit lifetime name
+{
+}
```
-`'_`, cannot be used as a lifetime identifier because it is a reserved for the
-anonymous lifetime. To fix this, use a lowercase letter such as 'a, or a series
-of lowercase letters such as `'foo`. For more information, see [the
-book][bk-no]. For more information on using the anonymous lifetime in rust
-nightly, see [the nightly book][bk-al].
+First, `'_` cannot be used as a lifetime identifier in some places
+because it is a reserved for the anonymous lifetime. Second, `&T`
+without an explicit lifetime name cannot also be used in some places.
+To fix them, use a lowercase letter such as `'a`, or a series
+of lowercase letters such as `'foo`. For more information about lifetime
+identifier, see [the book][bk-no]. For more information on using
+the anonymous lifetime in Rust 2018, see [the Rust 2018 blog post][blog-al].
Corrected example:
```
-fn longest<'a>(str1: &'a str, str2: &'a str) -> &'a str {
+fn underscore_lifetime<'a>(str1: &'a str, str2: &'a str) -> &'a str {
if str1.len() > str2.len() {
str1
} else {
str2
}
}
+
+fn and_without_explicit_lifetime<'foo, T>()
+where
+ T: Into<&'foo u32>,
+{
+}
```
[bk-no]: https://doc.rust-lang.org/book/appendix-02-operators.html#non-operator-symbols
-[bk-al]: https://doc.rust-lang.org/nightly/edition-guide/rust-2018/ownership-and-lifetimes/the-anonymous-lifetime.html
+[blog-al]: https://blog.rust-lang.org/2018/12/06/Rust-1.31-and-rust-2018.html#more-lifetime-elision-rules