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fn main() {
let s = String::from("hello"); // s 进入作用域
takes_ownership(s); // s 的值移动到函数里 ...
// ... 所以到这里不再有效
let x = 5; // x 进入作用域
makes_copy(x); // x 应该移动函数里,
// 但 i32 是 Copy 的,
// 所以在后面可继续使用 x
} // 这里x 先移出了作用域,然后是 s。但因为 s 的值已被移走,
// 没有特殊之处
fn takes_ownership(some_string: String) { // some_string 进入作用域
println!("{some_string}");
} // 这里some_string 移出作用域并调用 `drop` 方法。
// 占用的内存被释放
fn makes_copy(some_integer: i32) { // some_integer 进入作用域
println!("{some_integer}");
} // 这里some_integer 移出作用域。没有特殊之处