反射获取基本类型

反射：可以在运行时动态获取变量的相关信息
Import (“reflect”)

a. reflect.TypeOf，获取变量的类型，返回reflect.Type类型
b. reflect.ValueOf，获取变量的值，返回reflect.Value类型
c. reflect.Value.Kind，获取变量的类别，返回一个常量
d. reflect.Value.Interface()，转换成interface{}类型

var x float64 = 3.4
    fmt.Println("type:",reflect.TypeOf(x))
    v := reflect.ValueOf(x)
    fmt.Println("value:",v)
    fmt.Println("type:",v.Type())
    fmt.Println("kind:",v.Kind())
    fmt.Println("value:",v.Float())

    fmt.Println(v.Interface())
    fmt.Printf("value is %5.2e\n",v.Interface())
    y := v.Interface().(float64)
    fmt.Println(y)

输出如下：

type: float64
value: 3.4
type: float64
kind: float64
value: 3.4
3.4
value is 3.40e+00
3.4

反射获取结构体

package main

import (
    "fmt"
    "reflect"
)

type Student struct {
    Name  string
    Age   int
    score float32
}



func test(b interface{}) {
    t := reflect.TypeOf(b)
    fmt.Println(t)

    v := reflect.ValueOf(b)
    fmt.Println(v)

    k := v.Kind()
    fmt.Println(k)


    iv := v.Interface()
    fmt.Println(iv)

    stu,ok := iv.(Student)
    if ok {
        fmt.Printf("%v %T\n",stu,stu)
    }
}

func main() {
    var a Student = Student{
        Name:  "stu01",Age:   18,score: 92,}
    test(a)
}

输出如下：

PS E:\golang\go_pro\src\safly> go run demo.go
main.Student
{stu01 18 92}
struct
{stu01 18 92}
{stu01 18 92} main.Student
PS E:\golang\go_pro\src\safly>

Elem反射操作基本类型

用来获取指针指向的变量，相当于：
var a *int;

func main() {

    var b int = 1
    b = 200
    testInt(&b)
    fmt.Println(b)
}

//fv.Elem()用来获取指针指向的变量
func testInt(b interface{}) {
    val := reflect.ValueOf(b)
    val.Elem().SetInt(100)
    c := val.Elem().Int()

    fmt.Printf("get value interface{} %d\n",c)
    fmt.Printf("string val:%d\n",val.Elem().Int())
}

输出如下：

PS E:\golang\go_pro\src\safly> go run demo.go
get value  interface{} 100
string val:100
100
PS E:\golang\go_pro\src\safly>

反射调用结构体方法

package main

import (
    "fmt"
    "reflect"
)

type Student struct {
    Name  string
    Age   int
    score float32

}

func (s Student) Print(){
    fmt.Println(s)
}


func (s Student) Set(name string,age int,score float32){
    s.Age = age
    s.Name = name
    s.score = score
}


func TestStruct(a interface{}) {
    val := reflect.ValueOf(a)
    kd := val.Kind()

    fmt.Println(val,kd)
    if kd != reflect.Struct {
        fmt.Println("expect struct")
        return
    }
    //获取字段数量
    fields:= val.NumField()
    fmt.Printf("struct has %d field\n",fields)
    //获取字段的类型
    for i:=0;i<fields;i++{
        fmt.Printf("%d %v\n",i,val.Field(i).Kind())
    }
    //获取方法数量
    methods:=val.NumMethod()
    fmt.Printf("struct has %d methods\n",methods)

    //反射调用的Print方法
    var params []reflect.Value
    val.Method(0).Call(params)


}

func main() {
    var a Student = Student{
        Name:  "stu01",score: 92.8,}
    TestStruct(a)
    // fmt.Println(a)
}

输出如下：

PS E:\golang\go_pro\src\safly> go run demo.go
{stu01 18 92.8} struct
struct has 3 field
0 string
1 int
2 float32
struct has 2 methods
{stu01 18 92.8}
PS E:\golang\go_pro\src\safly>

Elem反射操作结构体

package main

import (
    "fmt"
    "reflect"
)

type Student struct {
    Name  string
    Age   int
    score float32

}

func (s Student) Print(){
    fmt.Println(s)
}


func (s Student) Set(name string,age int,score float32){
    s.Age = age
    s.Name = name
    s.score = score
}


func TestStruct(a interface{}) {
    val := reflect.ValueOf(a)
    kd := val.Kind()

    fmt.Println(val,kd)
    if kd!= reflect.Ptr && val.Elem().Kind() ==  reflect.Struct {
        fmt.Println("expect struct")
        return
    }
    //获取字段数量
    fields:= val.Elem().NumField()
    fmt.Printf("struct has %d field\n",fields)
    //获取字段的类型
    for i:=0;i<fields;i++{
        fmt.Printf("%d %v\n",val.Elem().Field(i).Kind())
    }
    //获取方法数量
    methods:=val.NumMethod()
    fmt.Printf("struct has %d methods\n",methods)

    //反射调用的Print方法
    var params []reflect.Value
    val.Elem().Method(0).Call(params)
}

func main() {
    var a Student = Student{
        Name:  "stu01",Age:   18,score: 92.8,}
    TestStruct(&a)
    // fmt.Println(a)
}

输出如下：

PS E:\golang\go_pro\src\safly> go run demo.go
&{stu01 18 92.8} ptr
struct has 3 field
0 string
1 int
2 float32
struct has 2 methods
{stu01 18 92.8}
PS E:\golang\go_pro\src\safly>

Elem反射获取tag

package main

import (
    "fmt"
    "reflect"
)

type Student struct {
    Name  string `json:"stu_name"`
    Age   int
    score float32

}

func (s Student) Print(){
    fmt.Println(s)
}


func (s Student) Set(name string,score float32){
    s.Age = age
    s.Name = name
    s.score = score
}


func TestStruct(a interface{}) {
    typ := reflect.TypeOf(a)

    tag := typ.Elem().Field(0).Tag.Get("json")
    fmt.Printf("Tag:%s\n",tag)
}

func main() {
    var a Student = Student{
        Name:  "stu01",}
    TestStruct(&a)
}

输出如下：

PS E:\golang\go_pro\src\safly> go run demo.go
Tag:stu_name
PS E:\golang\go_pro\src\safly>

练习例子

package main

import (
    "fmt"
    "reflect"
)

type T struct {
    A int
    B string
}

func main() {
    t := T{23,"skidoo"}
    s := reflect.ValueOf(&t).Elem()
    typeOfT := s.Type()
    for i := 0; i < s.NumField(); i++ {
        f := s.Field(i)
        fmt.Printf("%d: %s %s = %v\n",typeOfT.Field(i).Name,f.Type(),f.Interface())
    }
    s.Field(0).SetInt(77)
    s.Field(1).SetString("Sunset Strip")
    fmt.Println("t is now",t)
}

输出如下：

PS E:\golang\go_pro\src\safly> go run demo.go
0: A int = 23
1: B string = skidoo
t is now {77 Sunset Strip}
PS E:\golang\go_pro\src\safly>