可以先声明变量绑定，以后(然后)在初始化。 然而，这种形式很少使用，因为它可能导致使用未初始化的变量。
| fn main() { |
| // Declare a variable binding |
| let a_binding; |
| { |
| let x = 2; |
| // Initialize the binding |
| a_binding = x * x; |
| } |
| println!("a binding: {}", a_binding); |
| let another_binding; |
| // Error! Use of uninitialized binding |
| println!("another binding: {}", another_binding); |
| // FIXME ^ Comment out this line |
| another_binding = 1; |
| println!("another binding: {}", another_binding); |
| } |
