struct为何物

go中的struct可以实现oop中的类、方法。go语言中的struct成员可以是任何类型，如普通类型、复合类型、函数、struct、interface等。

入门

    //定义
    type User struct {
        name string
        email string
        password string
    }
    //声明
    var user User
    var userref *User
    fmt.Println(user)    //{} 默认初始化为零值
    fmt.Println(userref) //<nil> 未初始化
    userref = new(User)
    fmt.Println(userref) //&{  }

    //初始化
    user = User{name: "liming", email: "liming@gamil.com", password: "pw123456"}
    userref = &User{name: "liming", email: "liming@gamil.com", password: "pw123456"}
    fmt.Println(user)    //{liming liming@gamil.com pw123456}
    fmt.Println(userref) //&{liming liming@gamil.com pw123456}

    //简单写法
    user1 := User{name: "liming", email: "liming@gamil.com", password: "pw123456"}
    userref1 := &User{name: "liming", email: "liming@gamil.com", password: "pw123456"}
    fmt.Println(user1)    //{liming liming@gamil.com pw123456}
    fmt.Println(userref1) //&{liming liming@gamil.com pw123456}

    //引用与值的区别
    upUser(user1)
    upUser(userref1)//cannot use userref1 (type *User) as type User in argument to upUser
    upUserRef(userref1)
    fmt.Printf("name is %s,  %s", user1.name, userref1.name) //name is liming,  LIMING



    //递归struct

    type LinkedNode struct {
        data string
        su   *LinkedNode
    }

    type DoubleLinkedNode struct {
        pr   *DoubleLinkedNode
        data string
        su   *DoubleLinkedNode
    }

    type TreeNode struct {
        le   *TreeNode
        data string
        ri   *TreeNode
    }

进阶

构造方法

oop中 ， new Object（），go 通过工厂方法 NewStructName

//不强制使用构造函数，首字母大写
type File struct {
    fd       int
    filename string
}

func NewFile(fd int, name string) *File {
    if fd < 0 {
        return nil
    }
    return &File{fd, name}
}

//强制使用构造函数，首字母小写
type file1 struct {
    fd       int
    filename string
}

func NewFile1(fd int, name string) *file1 {
    if fd < 0 {
        return nil
    }
    return &file1{fd, name}
}

tag

可以为struct域加说明，这些说明可以通过反射获取

type TagType struct { // tags
 field1 bool “An important answer”
 field2 string “The name of the thing”
 field3 int “How much there are”
}

匿名域

每种类型只能有一个匿名域。可以用来实现oop中的继承

type anonymousStruct struct {
    name string
    int
    string
    File
}
    anonymous := new(anonymousStruct)
    anonymous.name = "hanmeimei"
    anonymous.int = 88
    anonymous.string = "english"
    anonymous.File.fd = 10               // or anonymous.fd = 10
    anonymous.File.filename = "xxoo.avi" //or anonymous.filename = "xxoo.avi"
    fmt.Println(anonymous)               //&{hanmeimei 88 english {10 xxoo.avi}}

方法

go语言中的oop很另类，类在go里面叫做receiver，receiver可以是除了interface之外的任何类型。方法和类并非组织在一起，传统的oop方法和类放在一个文件里面，而go语言只要在同一个包里就可，可分散在不同文件里。go的理念就是数据和实现分离

Methods are not mixed with the data definition (the structs): they are orthogonal to types; representation(data) and behavior (methods) are independent

go方法定义格式如下

func (recv receiver_type) methodName(parameter_list) (return_value_list) { … }

func (_ receiver_type) methodName(parameter_list) (return_value_list) { … }

func (this receiver_type) methodName(parameter_list) (return_value_list) { … }

func (self receiver_type) methodName(parameter_list) (return_value_list) { … }

oop调用 object.method ，go调用recv.Method()

定义非struct类型方法

type IntVector []int

func (v IntVector) Sum() (s int) {
    for _, x := range v {
        s += x
    }
    return
}

方法作用域

method和receiver必须在同一个包里定义

import “container/list”
//cannot define new methods on non-local type list.List
func (p *list.List) Iter() {
// …
}

hack方法

//hack
type myList struct {
    list.List //anonymous field
}
func (p *myList) Iter() {
    // …
}

reciever

reciever最好定义成指针的形式。对已非指针形式的reciever会自动转换成指针形式。如

func (u *User) Iter() {
    // …
}
u:=User{"liming",22}
u.Iter() //会转换成&User

getter setter

type Person struct {
 firstName string
 lastName string
}

func (p *Person) FirstName() string {
 return p.firstName
}
func (p *Person) SetFirstName(newName string) {
 p.firstName = newName
}