Scope and Shadowing

Variable bindings have a scope, and are constrained to live in a block. A
block is a collection of statements enclosed by braces {}. Also, variable
shadowing is allowed.

  1. fn main() {
  2.     // This binding lives in the main function
  3.     let long_lived_binding = 1;
  5.     // This is a block, and has a smaller scope than the main function
  6.     {
  7.         // This binding only exists in this block
  8.         let short_lived_binding = 2;
  10.         println!("inner short: {}", short_lived_binding);
  12.         // This binding *shadows* the outer one
  13.         let long_lived_binding = 5_f32;
  15.         println!("inner long: {}", long_lived_binding);
  16.     }
  17.     // End of the block
  19.     // Error! `short_lived_binding` doesn't exist in this scope
  20.     println!("outer short: {}", short_lived_binding);
  21.     // FIXME ^ Comment out this line
  23.     println!("outer long: {}", long_lived_binding);
  25.     // This binding also *shadows* the previous binding
  26.     let long_lived_binding = 'a';
  28.     println!("outer long: {}", long_lived_binding);
  29. }