Rust by Example

4.2 Scope and shadowing

Variables have local scope, and are constrained to live in a block (a block is a collection of statements enclosed by braces {}). Also, variable shadowing is allowed.

fn main() { // This variable lives in the main function let long_lived_variable = 1; // This is a block, and has a smaller scope than the main function { // This variable only exists in this block let short_lived_variable = 2; println!("inner short: {}", short_lived_variable); // This variable *shadows* the outer one let long_lived_variable = 5_f32; println!("inner long: {}", long_lived_variable); } // End of the block // Error! `short_lived_variable` doesn't exist in this scope println!("outer short: {}", short_lived_variable); // FIXME ^ Comment out this line println!("outer long: {}", long_lived_variable); }