golang method type definition

Golang is a very powerful programming language that supports object-oriented programming (OOP). In Golang, we can use methods to implement features such as encapsulation, inheritance, and polymorphism in object-oriented programming. A method refers to a function associated with a certain type, which can be called through the type, similar to member methods (Member Function) or instance methods (Instance Method) in other programming languages.

Methods in Golang are defined on a structure (Struct) or type (Type), and are closely related to the structure or type itself. Through methods, we can associate behavior with data, making the code more readable and concise.

Golang’s method type definitions mainly include the following:

1. Value type method (Value Method)
   Value type method refers to a function associated with a certain type. Its receiver is a value of this type. Modifications to the receiver within the method will not affect the original value.

For example, the following is the definition of a value type method:

type Rectangle struct {
    width, height float64
}

func (r Rectangle) area() float64 {
    return r.width * r.height
}

In this example, we define a Rectangle structure and a value type named area method. The receiver of this method is a Rectangle type value (r Rectangle), and returns a float64 type area.

When calling this method, we can call it through a Rectangle type value:

rect := Rectangle{width: 10, height: 5}
fmt.Println(rect.area())

2. Pointer type method (Pointer Method)
   Pointer type method refers to a certain A function associated with a type whose receiver is a pointer of that type. Modifying the receiver inside the method will affect the original value because the pointer points to the original value.

For example, the following is the definition of a pointer type method:

type Rectangle struct {
    width, height float64
}

func (r *Rectangle) scale(factor float64) {
    r.width = r.width * factor
    r.height = r.height * factor
}

In this example, we define a Rectangle structure and a pointer type named scale method. The receiver of this method is a pointer of type Rectangle (r *Rectangle) and has no return value. Inside the method, we multiply both the width and height properties of the structure by a factor.

When calling this method, we need to call it through a pointer to the Rectangle type:

rect := &Rectangle{width: 10, height: 5}
rect.scale(2)
fmt.Println(rect.width, rect.height)

3. Embedded Type Method
   The embedded type method refers to Make one type a field of another type and use that type's methods directly in methods. Embedded type methods are actually a method type definition unique to the Go language, which is equivalent to inheritance or mixed types in other languages.

For example, we can define an Animal type, then define a Cat type, and use the Animal type as an embedded field of the Cat type. In this way, the Cat type can directly use the methods of the Animal type.

type Animal struct {
    name string
}

func (a *Animal) move() {
    fmt.Println(a.name, "is moving")
}

type Cat struct {
    *Animal
}

func main() {
    cat := &Cat {
        Animal: &Animal {
            name: "Tom",
        },
    }
    cat.move()
}

In this example, we define an Animal type and a Cat type, and embed the Animal type into the Cat type as an anonymous field. In this way, the Cat type can directly use the methods of the Animal type.

When calling this method, we can directly call the move method of Cat type. Since the Cat type has an Animal type embedded in it, the move method is actually a method of that type.

Summary:
Golang supports multiple method type definitions such as value type methods, pointer type methods, and embedded type methods. By defining different types of methods, we can achieve different programming needs and bring more flexibility and convenience to Golang programming.

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