Static

A 'static lifetime is the longest possible lifetime, and lasts for
the lifetime of the running program. A 'static lifetime may also 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 static declaration.
  • Make a string literal which has type: &'static str.

See the following example for a display of each method:

  1. // Make a constant with `'static` lifetime.
  2. static NUM: i32 = 18;
  4. // Returns a reference to `NUM` where its `'static` 
  5. // lifetime is coerced to that of the input argument.
  6. fn coerce_static<'a>(_: &'a i32) -> &'a i32 {
  7.     &NUM
  8. }
  10. fn main() {
  11.     {
  12.         // Make a `string` literal and print it:
  13.         let static_string = "I'm in read-only memory";
  14.         println!("static_string: {}", static_string);
  16.         // When `static_string` goes out of scope, the reference
  17.         // can no longer be used, but the data remains in the binary.
  18.     }
  20.     {
  21.         // Make an integer to use for `coerce_static`:
  22.         let lifetime_num = 9;
  24.         // Coerce `NUM` to lifetime of `lifetime_num`:
  25.         let coerced_static = coerce_static(&lifetime_num);
  27.         println!("coerced_static: {}", coerced_static);
  28.     }
  30.     println!("NUM: {} stays accessible!", NUM);
  31. }

See also:

'static constants