Go structure method

#### Go  Structure method 
 I was so busy today that I didn't want to update the content , Later, it was completed ahead of schedule ,  So we still need to update ;  
 After all, persistence is not easy ! come on. , I believe that no matter you or me , There are some things you want to do , Then stick to it , Leave the rest to Providence ; 
 From yesterday to this morning, I have been dealing with wechat personal account payment ,*** It's probably that if an individual has no ability or permission to open wechat payment function ,
 And want to use the payment function of wechat , That may require some special treatment ,  The functions of Alipay are the same as above ***;  
 If you are interested in personal payment , You can call me ^_^;  
 I would like to recommend a song here   
 Original singing :  Zhao Fangjing   
--- 
#####  Method 
 In some cases, define methods :  Such as the behavior of the structure , It takes a method to complete ;  
Go  Methods in are applied to the specified data type ( Bind to the specified data type ), therefore *** Custom types can have methods , It's not just the structure ***;  
 Method declaration and call :  
type A struct {
    Name string  
}  
func (a A) say(){  
   fmt.Println(a.Name)   
}
 explain :  
1. func(a A) say() {}  Represents a structure A There's a way , The name is say
2. (a A)  reflect say  Methods and A  Type binding   
 Case study :  

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

package main import "fmt" type Person struct {    Name string    Age int } func (p Person) say(){    fmt.Printf("I am %s and %d years old\n",p.Name,p.Age) } func main(){    var p Person    p.Name = "aaa"    p.Age = 11    var p2 Person    p2.Name = "bbb"    p2.Age = 22    // Invoking an instance method    p.say() // I am aaa and 11 years old    p2.say() //I am bbb and 22 years old }

　　

 explain :  
1. say  Methods and Person  Type binding 
2. say  Method can only pass through Person  Type to call , Can't call directly , You can't use other types of variables to call ; 
3. say  Method and others OOP  The language is very different ,*** There are no static methods ***; 
4. func (p Person) say(){} p  It means which Person  The instance , This p  It's a copy of it , Similar to function arguments ;  
5. p*** Called the receiver ***, You can customize , It is generally recommended to name some types that can be intuitively experienced ;  
---
 Let's try another example : 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

package main import (    "fmt" ) type Student struct {    Name string    Age int    Skills []string } // Here is a similar quote func (s *Student)Learn(skill string) {    // Through the study , Know a skill    // append The bottom layer will automatically make    s.Skills = append(s.Skills,skill) } func (s Student) Show(){    for _,skill := range s.Skills {       fmt.Printf("I am %s,I am %d years old,and %sing is my skill\n",s.Name,s.Age,skill)    } } func main(){    var s1 Student    s1.Name = " Xiao Ming "    s1.Age = 20    s1.Learn("fish")    s1.Learn("learn")    var s2 Student    s2.Name = " Xiaohong "    s2.Age = 18    s2.Learn("Sing")    s2.Learn("paint")    // Calling method    s1.Show()    s2.Show()    //I am Xiao Ming ,I am 20 years old,and fishing is my skill    //I am Xiao Ming ,I am 20 years old,and learning is my skill    //I am Xiaohong ,I am 18 years old,and Singing is my skill    //I am Xiaohong ,I am 18 years old,and painting is my skill }

　　

 explain :  
 The above small example integrates the previous knowledge , There is also the knowledge to be learned in this section , After learning this section, you should be able to understand ;  
#####  The principle of method calling and parameter passing mechanism  
 The mechanism of method calling and parameter passing is basically the same as that of function , The difference is that when a method is called , The variable that invokes the method will also be passed to the method as an argument ;  
 If the receiver is a value type, copy the value , If the receiver is a reference type, copy the address ;  

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

package main import "fmt" type Student struct {    Name string    Age int } func (s Student) setName(){    // The receiver is a copy of the instance variable , Changing a value within a method does not affect the original value    s.Name = "aaaaaa" } func (s *Student) setAge(){    // The recipient is a copy of the instance variable address , Changing a value within a method changes the original value    s.Age = 21 } func main(){    var s1 Student    var s2 Student    s1.Name = "a"    s1.Age = 10    s2.Name = "b"    s2.Age = 10    s1.setName()    fmt.Println(s1)// {a 10}    s2.setAge()    fmt.Println(s2) //{b 21} }

　　

 Method considerations : 
1.  A structure is a value type , Following the value type passing mechanism in method calls ;   
2.  If you need to change the value of the structure variable , Similar to the above example , Handle through structure pointer ; 
3. Go  The method in acts on the method of the specified data type ( Bind to the specified data type );
4.  The rules of the control scope of a method are the same as those of a function , Method names start in lowercase , Can only be accessed within this package , Method initial is capitalized , It can be accessed in this package and other packages ;  
5.  If a structure implements String()  Method , that fmt.Println()  The default is to call String  Method to output ;  
6.  When the method receiver is a value type , You can call... Directly with a pointer type variable , The reverse can also ;  
7.  Whether the receiver is a value type or a reference type, you can directly use the instance variable to call the method ; 
 Case study :  

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

package main import "fmt" type Student struct {    Name string    Age int } // You can also call this method using a value type func (s *Student) setName(){    s.Name = "bbbb" } // You can also call this method using a pointer type func (s Student) showName(){    fmt.Println(s.Name) } // Default fmt.Println This method is called func (s Student) String() string{    return fmt.Sprintf("I am %s,i am %d years old",s.Name,s.Age) } func main(){    var s Student    s.Name = "a"    s.Age = 20    fmt.Println(s) // I am a,i am 20 years old    s.setName() // The call receiver of value type is a method of pointer type    s.showName() // bbbb    fmt.Println(s) // I am bbbb,i am 20 years old    var s1 *Student = new(Student)    s1.Name = "b"    s1.Age = 10    fmt.Println(s1) // I am b,i am 10 years old    s1.setName() //    s1.showName() // bbbb The call receiver of pointer type is a method of value type    // Here we need to say     // Standard call The way should be     (*s1).showName()     // Go The compiler automatically makes reference at the bottom , So it can be simplified to s1.showName     // All in all , Whether it is a pointer receiver or a value receiver , Unified use case . The method name can ;    fmt.Println(s1) //I am bbbb,i am 10 years old }

　　

---
 To sum up : 
 Whatever the call form ( Whether the caller is a value type or a reference type ), It really determines whether it is value copy or address copy , It depends on the type of receiver of the method ;  
 Such as : (p Person)  Then you copy the value ,(p *Person)  It's a copy of the address ;  
 Today's content , It's a little twisted , That's all for the moment , Learning a new programming language requires discarding other programming styles , Hope to make progress together ;
 The latest content will be posted on the personal wechat official account , Welcome to exchange and learn together