4.7 方法和关联函数 (Methods and Associated Functions)

Methods are similar to functions in that we declare them with the fn keyword and they have parameters and return a value. However, unlike functions, Methods are defined within the context of a struct (or enum), and either refers to that type or mutates it. The first parameter of a method is always self, which represents the instance of the struct the method is being called on.

方法与函数类似，我们用 fn 关键字声明它们，它们有参数并返回一个值。然而，与函数不同的是，方法 是在一个结构（或穷举）的上下文中定义的，并且可以引用该类型或对其进行变化。方法的第一个参数总是 self，它代表方法被调用的结构实例。

Associated functions are very similar to methods, in that they are also defined in the context of a struct or enum, but they do not actually use any of the data in the struct and as a result do not take self as a parameter. Associated functions could be standalone functions, but they are included in a specific type for organizational or semantic reasons.

关联函数 与 方法 非常相似，因为它们也是在解构或穷举的上下文中定义的，但它们实际上并不使用解构中的任何数据，因此不把 self 作为参数。关联函数可以是独立的函数，但出于组织或语义的原因，它们被包含在特定的类型中。

To declare methods and associated functions for a struct or enum, use an impl block. Here, impl stands for implementation.

要为一个结构或穷举，声明方法和关联函数，请使用 impl块。这里，impl代表实现。

script;

struct Foo {
    bar: u64,
    baz: bool,
}

impl Foo {
    // this is a _method_, as it takes `self` as a parameter.
    fn is_baz_true(self) -> bool {
        self.baz
    }

    // this is an _associated function_, since it does not take `self` as a parameter.
    fn new_foo(number: u64, boolean: bool) -> Foo {
        Foo {
            bar: number,
            baz: boolean,
        }
    }
}

fn main() {
    let foo = Foo::new_foo(42, true);
    assert(foo.is_baz_true());
}

To call a method, simply use dot syntax: foo.iz_baz_true().

要调用一个方法，只需使用点语法： foo.iz_baz_true()。

Similarly to free functions, methods and associated functions may accept ref mut parameters. For example:

与自由函数类似，方法和相关函数可以接受ref mut参数。例如：

struct Coordinates {
    x: u64,
    y: u64,
}

impl Coordinates {
    fn move_right(ref mut self, distance: u64) {
        self.x += distance;
    }
}

and when called:

以及当调用时：

    let mut point = Coordinates { x: 1, y: 1 };
    point.move_right(5);
    assert(point.x == 6);
    assert(point.y == 1);