Explicit annotation
The borrow checker uses explicit lifetime annotations to determine how long references should be valid. In cases where lifetimes are not elided1, Rust requires explicit annotations to determine what the lifetime of a reference should be. The syntax for explicitly annotating a lifetime uses an apostrophe character as follows:
foo<'a>
// `foo` has a lifetime parameter `'a`Similar to closures, using lifetimes requires generics.
Additionally, this lifetime syntax indicates that the lifetime of foo
may not exceed that of 'a. Explicit annotation of a type has the form
&'a T where 'a has already been introduced.
In cases with multiple lifetimes, the syntax is similar:
foo<'a, 'b>
// `foo` has lifetime parameters `'a` and `'b`In this case, the lifetime of foo cannot exceed that of either 'a or 'b.
See the following example for explicit lifetime annotation in use:
elision implicitly annotates lifetimes and so is different.