变量绑定

Rust 通过静态类型提供类型安全。变量绑定可以在声明时进行类型注释。但是，在大多数情况下，编译器能够从上下文中推断出变量的类型，从而大大减少了注释负担。

可以使用 let 绑定将值（如字面量）绑定到变量。

fn main() {
    let an_integer = 1u32;
    let a_boolean = true;
    let unit = ();

    // copy `an_integer` into `copied_integer`
    let copied_integer = an_integer;

    println!("An integer: {:?}", copied_integer);
    println!("A boolean: {:?}", a_boolean);
    println!("Meet the unit value: {:?}", unit);

    // The compiler warns about unused variable bindings; these warnings can
    // be silenced by prefixing the variable name with an underscore
    let _unused_variable = 3u32;

    let noisy_unused_variable = 2u32;
    // FIXME ^ Prefix with an underscore to suppress the warning
    // Please note that warnings may not be shown in a browser
}