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 {}
.
fn main() { // This binding lives in the main function let long_lived_binding = 1; // This is a block, and has a smaller scope than the main function { // This binding only exists in this block let short_lived_binding = 2; println!("inner short: {}", short_lived_binding); } // End of the block // Error! `short_lived_binding` doesn't exist in this scope println!("outer short: {}", short_lived_binding); // FIXME ^ Comment out this line println!("outer long: {}", long_lived_binding); }
Also, variable shadowing is allowed.
fn main() { let shadowed_binding = 1; { println!("before being shadowed: {}", shadowed_binding); // This binding *shadows* the outer one let shadowed_binding = "abc"; println!("shadowed in inner block: {}", shadowed_binding); } println!("outside inner block: {}", shadowed_binding); // This binding *shadows* the previous binding let shadowed_binding = 2; println!("shadowed in outer block: {}", shadowed_binding); }