rust - 什么时候在方法中使用 self、&self 和 &mut self？

Question

采用 self 的方法与采用 &self 甚至 &mut self 的方法有什么区别？

例如

impl SomeStruct {
    fn example1(self) { }
    fn example2(&self) { }
    fn example3(&mut self) { }
}

假设我想实现一个将结构漂亮地打印到标准输出的方法，我应该采用 &self 吗？我想 self 也可以吗？我不确定什么时候使用什么。

Answer 1

来自示例in the book (只是分成三个单独的段落并标记可能使它更清楚):

&self: We’ve chosen &self here for the same reason we used &Rectangle in the function version: we don’t want to take ownership, and we just want to read the data in the struct, not write to it.

&mut self: If we wanted to change the instance that we’ve called the method on as part of what the method does, we’d use &mut self as the first parameter.

self: Having a method that takes ownership of the instance by using just self as the first parameter is rare; this technique is usually used when the method transforms self into something else and you want to prevent the caller from using the original instance after the transformation.

或者换句话说:区别与SomeStruct、&SomeStruct和&mut SomeStruct完全相同。

Say I want to implement a method that pretty prints the struct to stdout, should I take &self? I guess self also works?

如您所见，这正是 &self 的情况。如果您使用 self(或 &mut self)，该方法可能仍会编译，但它只能在更受限制的情况下使用。