Static
Rust has a few reserved lifetime names. One of those is 'static. You
might encounter it in two situations:
Both are related but subtly different and this is a common source for confusion when learning Rust. Here are some examples for each situation:
Reference lifetime
As a reference lifetime 'static indicates that the data pointed to by
the reference lives for the entire lifetime of the running program.
It can still be coerced to a shorter lifetime.
There are two ways to make a variable with 'static lifetime, and both
are stored in the read-only memory of the binary:
- Make a constant with the
staticdeclaration. - Make a
stringliteral which has type:&'static str.
See the following example for a display of each method:
Trait bound
As a trait bound, it means the type does not contain any non-static references. Eg. the receiver can hold on to the type for as long as they want and it will never become invalid until they drop it.
It's important to understand this means that any owned data always passes
a 'static lifetime bound, but a reference to that owned data generally
does not:
The compiler will tell you:
error[E0597]: `i` does not live long enough
--> src/lib.rs:15:15
|
15 | print_it(&i);
| ---------^^--
| | |
| | borrowed value does not live long enough
| argument requires that `i` is borrowed for `'static`
16 | }
| - `i` dropped here while still borrowed