The reflection of Go language

Reflection reflex

• Reflection can greatly increase the flexibility of the program, so that interface{} has a greater scope of play
• Reflection uses the TypeOf and valueof functions to get target object information from the interface
• Reflection will use anonymous fields as separate fields (anonymous field nature)
• You want to use reflection to modify the state of an object, if Interface.data is settable, which is pointer-interface
• The method can be called "dynamic" by reflection

Example 1, using reflection to obtain attribute information, method information

Reflection exercises//Get field type information, method information, property information package Mainimport ("FMT" "reflect") type User struct {Id int Name string Ag e int}func (user user) Hello () {fmt. Println ("Hello World")}func main () {User: = User{id:2, Name: "Xiaoqiang", age:30} info (user)}//define a method//This method receives an empty interface// In this case, actually any type can receive the Func info (o interface{}) {//Get O of type T: = reflect. TypeOf (o) fmt. Println ("Type:\t", T.name ())//remove type, you need to verify the type,//See if it is the specified type if K: =t.kind (); K! = reflect. struct {//if it is not a specified struct type, it is necessary to do//exception handling FMT.        Println ("The type of the input parameter does not match!") return}//Get the property of O V: = reflect. ValueOf (o) fmt. Println ("fields:\n")//Start traversal, output field for I: = 0; I < T.numfield (); i++ {//Gets the property subscript f: = T.field (i) Val: = V.field (i). Interface ()//The name of the output attribute, type, corresponding to the value FMT. Printf ("%6s:%v =%v\n", F.name, F.type, Val)}//start getting basic information for the method for i:=0; I<t.nummethod (); i++ {m: = T.method (i) fmt. Printf ("%6s:%v\n", M.name, M.type)}} 

2. How does reflection get anonymous fields?

//反射 是如何处理 匿名字段的？package mainimport (    "reflect"    "fmt")type Stu struct {    Id int    Name string    Age int}type Man struct {    //这里你要注意一下，你创建的属性，是有顺序的，是有下标的    //如Stu 下标 就是0， title下标就是1    // Stu 就是匿名属性    Stu    title string}func main() {    //注意，对匿名字段进行初始化时的方式，其实本质上跟其他属性是一样的    m := Man{Stu:Stu{Id:2,Name:"Jack",Age:19}, title:"Manager"}    t := reflect.TypeOf(m)    //取匿名字段的方式    //FieldByIndex 方法，传入的是一个切片slice类型    //第1个0，表示，匿名字段在Man中的下标位置    //第2个0，表示，你要取匿名字段中哪个属性的下标    fmt.Printf("%#v\n", t.FieldByIndex([]int{0,0})) //取的是id    fmt.Printf("%#v\n", t.FieldByIndex([]int{0,1})) //取的是Name    fmt.Printf("%#v\n", t.FieldByIndex([]int{0,2})) //取的是Age}

3. Modify the basic type by reflection

//如果通过反射，对基本类型进行修改package mainimport (    "reflect"    "fmt")func main() {    //下面测试，对基本类型的修改 操作    x := 456    //传递的参数是  地址    v := reflect.ValueOf(&x)    //Elem方法，是取出元素值来，然后通过setint方法，进行重新设置    v.Elem().SetInt(789)    fmt.Println(x)}

4. Modification of complex types by reflection

//如果通过反射，对复杂类型进行修改package mainimport (    "reflect"    "fmt")type Teac struct {    Id int    Name string    Age int}func main() {    teac := Teac{Id:5,Name:"Ant-man",Age:23}    fmt.Println("teac:\t", teac)    //传递的是 地址哦    Set(&teac)    fmt.Println("teac:\t", teac)}func Set(o interface{}) {    v := reflect.ValueOf(o)    if v.Kind() == reflect.Ptr && !v.Elem().CanSet() {        fmt.Printf("xxx")        return    }else{        v = v.Elem()    }    // 通过FieldByName 这个方法，直接输入 名称，来获取    f := v.FieldByName("Name")    //校验，是否取到Name属性的值    if !f.IsValid() {        fmt.Printf("BAD")        return    }    //然后，再校验，类型是否匹配    if f.Kind() == reflect.String {        f.SetString("Iron Man")    }}

5. Dynamic invocation of the method through reflection

//通过反射，进行方法的调用，相当于动态调用了package mainimport (    "fmt"    "reflect")type Teacher struct {    Id int    Name string    Age int}//通过receiver将Show方法，跟Teacher类型，进行绑定func (teacher Teacher)Show(name string) {    fmt.Println("hello, ", name, ", my name is ", teacher.Name)}//注意======目前没有发现====如何通过====反射===来获取=====私有方法func (teacher Teacher)info(){    fmt.Println("=====")}func main() {    teacher := Teacher{Id:34, Name:"Thor",Age:34}    teacher.Show("Hawkeye")    //下面通过反射，调用show方法    v := reflect.ValueOf(teacher)    //获取show方法    m := v.MethodByName("Show")    //校验一下，是否获取到show方法呢    if !m.IsValid() {        fmt.Printf("=======没有获取到制定的方法====")        return    }    //参数必须是切片类型    //reflect.Value{}   这里面，可以设定多个参数类型    //目前，我们这里只有一个string类型的参数    //    args := []reflect.Value{reflect.ValueOf("Hulk")}    m.Call(args)}

The reflection of Go language