Go language foundation ----- 06 ----- anonymous fields, fields with the same name

One Anonymous field 、 Fields with the same name

1 The function and initialization of anonymous fields

• 1）go Anonymous fields in are only types , Isn't there a name .
• 2） The role of anonymous fields ： because go No packaging 、 Inherit 、 The concept of polymorphism , however go It can also be object-oriented programming , Because there are anonymous fields . For example, the following ,Student Inherited through anonymous fields Persion All members of .

Actually went to school C Of all know , It's just a simple structure nesting , But in go It's so tall .

type Persion struct {
    
	name string
	sex byte
	age int
}

//  The declarations of ordinary variables are var keyword , There is no need for var
type Student struct {
    
	Persion	//  Anonymous field , Only type , Isn't there a name . It inherited Persion All members of 
	id int
	addr string
}

• 3） Initialization of anonymous fields

package main

import "fmt"

type Persion struct {
    
	name string
	sex byte
	age int
}

//  The declarations of ordinary variables are var keyword , There is no need for var
type Student struct {
    
	Persion	//  Anonymous field , Only type , Isn't there a name . It inherited Persion All members of 
	id int
	addr string
}

func main(){
    
	// 1.  Sequence initialization 
	var s1 Student = Student{
    Persion{
    "hh", 'w',24}, 1, "sz"}
	fmt.Println("s1 = ", s1)

	// 2.  Automatic derivation type 
	s2 := Student{
    Persion{
    "cc", 'w',24}, 2, "sz"}
	fmt.Printf("s2 = %+v\n", s2)// %+v Indicates that the display is more detailed 

	// 3.  Initialize members 
	s3 := Student{
    id:1}
	fmt.Printf("s3 = %+v\n", s3)

	//  When assigning values to members , The corresponding field name must be manually added before each value , Otherwise the newspaper mixture of field:value and value initializers
	s4 := Student{
    Persion: Persion{
    name: "ll", sex: 'w'}, id: 1}
	//s4 := Student{Persion{"cc", 'w'}, 2}// err:mixture of field:value and value initializers
	fmt.Printf("s4 = %+v\n", s4)

	// 4.  Use member operations to specify member initialization 
	var s5 Student
	s5.Persion.name = "qq"	//  Write at this time s5.name It's the same 
	s5.name = "mm"
	s5.age = 24
	s5.id = 1
	fmt.Printf("s5 = %+v\n", s5)
}

result ：

2 Fields with the same name

1） A field with the same name has a member in an anonymous field , There is also a member with the same name outside the anonymous field .

type Persion struct {
    
	name string
	sex byte
	age int
}

//  The declarations of ordinary variables are var keyword , There is no need for var
type Student struct {
    
	Persion	//  Anonymous field , Only type , Isn't there a name . It inherited Persion All members of 
	id int
	addr string
	name string //  Fields with the same name , because Persion There's one in there, too name. The compiler operates according to the principle of proximity , That is, this member has high priority .
}

• 2） When there is a field with the same name , The compiler will search according to the principle of proximity . If found in this scope , Direct use , If not, go to the inherited structure to find .

package main

import "fmt"

type Persion struct {
    
	name string
	sex byte
	age int
}

//  The declarations of ordinary variables are var keyword , There is no need for var
type Student struct {
    
	Persion	//  Anonymous field , Only type , Isn't there a name . It inherited Persion All members of 
	id int
	addr string
	name string //  Fields with the same name , because Persion There's one in there, too name. The compiler operates according to the principle of proximity , That is, this member has high priority .
}

func main(){
    
	var s1 Student
	s1.name = "hh"				//  The operation is Student Of name, instead of Persion Of name
	s1.id = 1
	s1.addr = "sz"
	s1.Persion.name = "perName"	//  Display operation is required 
	s1.Persion.age = 22
	s1.Persion.sex = 'w'		// ascii Code value print character type 
	fmt.Printf("s1 = %+v\n", s1)
}

3 Unstructured type anonymous field

• 1） In fact, unstructured type anonymous fields and 1 The anonymous fields mentioned above are the same , But these types are not structures , It's usually the basic data type , for example int、short these .
  Here is just to impress everyone .

package main

import "fmt"

type Persion struct {
    
	name string
	sex byte
	age int
}

//  The declarations of ordinary variables are var keyword , There is no need for var
type Student struct {
    
	Persion	//  Anonymous field , Only type , Isn't there a name . It inherited Persion All members of 
	int
	// string //  Cannot have anonymous fields of the same type , Will report a mistake error: duplicate field string
	string //  Fields with the same name , because Persion There's one in there, too name. The compiler operates according to the principle of proximity , That is, this member has high priority .
}

func main(){
    
	var s1 Student
	s1 = Student{
    Persion{
    "h", 'w', 24}, 111, "hhh"}
	fmt.Println("s1 = ", s1)
}

4 Structure pointer anonymous field

• 1） Empathy , Structure pointer anonymous field and 1 It's the same as what I said , Here is just to impress everyone , Specify how to use .

package main

import "fmt"

type Persion struct {
    
	name string
	sex byte
	age int
}

//  The declarations of ordinary variables are var keyword , There is no need for var
type Student struct {
    
	*Persion	//  Anonymous field , Only type , Isn't there a name . It inherited Persion All members of 
	id int
	addr string
}

func main(){
    
	// 1.  Don't use new The way 
	s1 := Student{
    &Persion{
    "hh", 'w', 24}, 1, "sz"}
	fmt.Println(s1.name, s1.sex, s1.age, s1.id, s1.addr)

	// 2.  Use new The way 
	var s2 Student
	s2.Persion = new(Persion)
	s2.name = "cc"
	s2.sex = 'w'
	s2.age = 24
	s2.id= 1
	s2.addr = "sz"
	fmt.Println(s2.name, s2.sex, s2.age, s2.id, s2.addr)
}