Golang function method value and method expression implementation method

Method value and method expression implementation method of Golang function

In Golang, functions are first-class citizens. This means that functions are syntactically just like other values ​​and can be stored in variables, passed to functions, and returned from functions. In addition to this, Golang also provides methods to extend the behavior of types. A method is a special function that exists on a type and can access the fields and methods of the type. In this article, we will discuss the method value and method expression implementation methods of Golang functions.

Method value and method expression

First, let us take a look at method value and method expression. The method value is a function value to which a receiver is bound. It is similar to a normal function, but it also contains a receiver, which is specified when the function is defined. Therefore, the method value can be passed and stored like a normal function, but it also retains a reference to the receiver.

The following is an example:

type Rect struct {
  width, height float64
}

func (r Rect) Area() float64 {
  return r.width * r.height
}

func main() {
  r := Rect{3, 4}

  // 获取 Rect 类型的 Area 方法值
  f := r.Area
  // 调用方法值
  fmt.Println(f())
}

In the above example, we define a type named Rect and define a type named # for it. ##Area method. This Area method receiver is of type Rect, so it can only be called by instances of Rect. In the main function, we create a Rect instance r and obtain its Area method value and store it in in a variable named f. Since f is a function value, we can call it like a normal function, but it also retains a reference to the r instance, so it is automatically passed in ## when called. #r. Similar to method values, method expressions are function expressions bound to receivers. It is similar to a method value, but it does not depend on any instance and can be called when there is no instance. Method expressions use type names as receivers.

The following is an example of using a method expression:

type Rect struct {
  width, height float64
}

func (r Rect) Area() float64 {
  return r.width * r.height
}

func main() {
  // 获取 Rect 类型的 Area 方法表达式
  f := Rect.Area
  fmt.Println(f(Rect{3, 4}))
}

In the above example, we use

to get the Rect type ##Area Method expression. Since the method expression does not depend on any instance, we can directly pass a Rect instance and it will automatically be used as the receiver when called. How to implement methods

type Rect struct {
  width, height float64
}

func (r Rect) Scale(factor float64) {
  r.width *= factor
  r.height *= factor
}

func main() {
  r := Rect{3, 4}
  r.Scale(2)
  fmt.Println(r.width, r.height)
}

Scale

factor and multiplies the Rect's width and height by it. When the method is called, due to the use of a value receiver, the value of the r instance is copied into the method and modified. So even if the width and height are modified within the method, we still have access to the original values ​​outside the function. The following is an example of using a pointer receiver:

type Rect struct {
  width, height float64
}

func (r *Rect) Scale(factor float64) {
  r.width *= factor
  r.height *= factor
}

func main() {
  r := &Rect{3, 4}
  r.Scale(2)
  fmt.Println(r.width, r.height)
}

Scale

factor and multiplies the Rect's width and height by it. When a method is called, thanks to the use of a pointer receiver, the pointer to the r instance is passed into the method and its fields can be modified directly. Therefore, the modified value can also be accessed outside the function. Conclusion

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