An article teaches you the basics of reflection in Go language

What is reflection

Reflection, um..., means reverse, that is, turning things over.

For example, a very simple code like this.

var a int = 3
fmt.Println(a)

Of course we know that the avariable isint type, but thinking about it the other way around, how does the program know that a is What about the int type? ? ?

At this time, you need to use reflection.

Sample code

v := reflect.TypeOf(a)
fmt.Println(v)

The two codes are combined into one execution result

The second line of code successfully restored the variable a to int type.

What? ? ? What use are you to me? ? ? ,Um. . . To be honest, I don’t use it too much, but I have to know how to do it.

Reflection (reflect package)

In Go, any variable , both have concrete types and concrete values ​​, just like var a int = 3, The specific type is int, The specific value is 3.

So, the specific type of the variable belongs to reflect.Type , the specific value of the variable belongs to reflect.Value.

And Go provides

• ##reflect.TypeOf Get the specific type.

• ##reflect.ValueOfGet the specific value.

TypeOf

##TypeOf

method can get the # of the variable ##Specific type. There is a need to define a function that can receive any type of data and print the variable type through reflection.

示例代码

函数

func reflectType(x interface{}) {
    v := reflect.TypeOf(x)
    fmt.Printf("你传入的变量类型是:%v\n"，v)
}

main

func main() {
    var a int = 666
    var b float64 = 3.14
    var c string = "hello world"
    var d [3]int = [3]int{1，2，6}
    var e []int = []int{1，2，6，88}
    var f map[string]interface{} = map[string]interface{}{
        "Name":"张三"，
        "Age":18，
}
    reflectType(a)
    reflectType(b)
    reflectType(c)
    reflectType(d)
    reflectType(e)
    reflectType(f)
}

执行结果

通过reflect.TypeOf方法，完美解决上述需求。

TypeOf 的Name和Kind

这个是啥意思呢??这个在结构体中比较好体现。

简答来说就是TypeOf返回的太笼统了，还有更加细化的类型，通过这俩属性获取。

示例代码

函数

func reflectType(x interface{}) {
v := reflect.TypeOf(x)
fmt.Printf("你传入的变量类型是:%v | Name:%v | Kind:%v\n"， v， v.Name()， v.Kind())
}

结构体

type Student struct {
    Name string
    Age int
}

main

func main() {
    var a int
    var b *int
    var c []int
    var d map[string]interface{}
    var e Student
    reflectType(a)
    reflectType(b)
    reflectType(c)
    reflectType(d)
    reflectType(e)
}

执行结果

总结

经过对比，会发现几个特殊问题。

如果变量是指针类型，Name为空，Kind是ptr。

If the variable is a reference type (slice and map) type, Name is empty, only Kind.

If the variable is a structure, Name is the structure name, Kind is struct.

ValueOf

TypeOf can only get the ## of the variable in reverse #Specific type, but you cannot get the specific value, which is a bit unkind.

所以ValueOf就来解决这个问题了，但是ValueOf牛叉的是，它里面还包括了变量类型。

注:ValueOf和TypeOf的Kind属性返回内容是一摸一样的。

需求:定义一个函数，可以接收任意类型，通过反射得出变量类型和变量值。

函数

func reflectType(x interface{}) {
    v := reflect.ValueOf(x)
    k := v.Kind()
    switch k {
    case reflect.Int:
        fmt.Printf("我是Int类型，我的值是%v\n"，v.Int())
    case reflect.Slice:
        fmt.Printf("我是切片类型，我的值是%v\n"，v.Slice(1，2))
    case reflect.Map:
        fmt.Printf("我是切片类型，我的值是%v\n"，v.MapKeys())
    //case :可以继续case下去
  }
}

main

func main() {
  var a int = 1
  var c []int = []int{1， 5， 7， 19}
  var d map[string]interface{} = map[string]interface{}{
    "Name": "你好"，
    "Age":  18，
  }
  var e Student
  reflectType(a)


  reflectType(c)
  reflectType(d)
  reflectType(e)
}

执行结果

通过反射设置值

反射还有一个用途，就是动态的修改变量值，可能你暂时体会不到，但是语法还是要学的。

通过反射设置值，需要用到Elem方法，并且传入的必须是指针。

示例代码

函数

func reflectSetValue(x interface{}) {
  v := reflect.ValueOf(x)
  //kind也必须是Elem调用
  var k = v.Elem().Kind()
  switch k {
  case reflect.Int:
    //反射修改必须通过Elem
    v.Elem().SetInt(200)
  }
}

main

func main() {
  var a int = 10
  fmt.Printf("a的值:%v\n"， a)
  //反射修改值传入的必须是地址
  reflectSetValue(&a)
  fmt.Printf("a的值:%v\n"， a)
}

执行结果

Summary

We have learned the basic reflection of GoTypeOf, Name and Kind of TypeOf,ValueOf, Set the value via reflection.

whereKind is in Type# Both ## and ValueOf are available, usually TypeOf and ValueOfUse together for better results!

Reflection may not be easy to understand, so you must work harder! persist in! !

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