借用和生命

Rust 中的所有值都有生命週期。值的生命週期跨越程式碼段，將值引入到移動的位置或包含範圍的末尾

{
    let x = String::from("hello"); //             +
    // ...                                        :
    let y = String::from("hello"); //      +      |
    // ...                                 :      :
    foo(x) // x is moved                   |      = x's lifetime
    // ...                                 :
} //                                       = y's lifetime

無論何時借用一個值，結果引用的生命週期都與借用值的生命週期相關聯：

{
    let x = String::from("hello");
    let y = String::from("world");
    // when we borrow y here, the lifetime of the reference
    // stored in foo is equal to the lifetime of y
    // (i.e., between let y = above, to the end of the scope below)
    let foo = &y;
    // similarly, this reference to x is bound to the lifetime
    // of x --- bar cannot, for example, spawn a thread that uses
    // the reference beyond where x is moved below.
    bar(&x);
}