Was nützt die Golang-Reflexion?

type Foo struct {
    A int 
    B string
}

var x Foo

func DoSomething(f Foo) {
  fmt.Println(f.A, f.B)
}

varType := reflect.TypeOf(var)

package main
import (
    "fmt"
    "reflect"
)
type FooIF interface {
    DoSomething()
    DoSomethingWithArg(a string)
    DoSomethingWithUnCertenArg(a ... string)
}
type Foo struct {
    A int
    B string
    C struct {
        C1 int
    }
}
func (f *Foo) DoSomething() {
    fmt.Println(f.A, f.B)
}
func (f *Foo) DoSomethingWithArg(a string) {
    fmt.Println(f.A, f.B, a)
}
func (f *Foo) DoSomethingWithUnCertenArg(a ... string) {
    fmt.Println(f.A, f.B, a[0])
}
func (f *Foo) returnOneResult() int {
    return 2
}
func main() {
    var simpleObj Foo
    var pointer2obj = &simpleObj
    var simpleIntArray = [3]int{1, 2, 3}
    var simpleMap = map[string]string{
        "a": "b",
    }
    var simpleChan = make(chan int, 1)
    var x uint64
    var y uint32
    varType := reflect.TypeOf(simpleObj)
    varPointerType := reflect.TypeOf(pointer2obj)
    // 对齐之后要多少容量
    fmt.Println("Align: ", varType.Align())
    // 作为结构体的`field`要对其之后要多少容量
    fmt.Println("FieldAlign: ", varType.FieldAlign())
    // 叫啥
    fmt.Println("Name: ", varType.Name())
    // 绝对引入路径
    fmt.Println("PkgPath: ", varType.PkgPath())
    // 实际上用了多少内存
    fmt.Println("Size: ", varType.Size())
    // 到底啥类型的
    fmt.Println("Kind: ", varType.Kind())
    // 有多少函数
    fmt.Println("NumMethod: ", varPointerType.NumMethod())
    // 通过名字获取一个函数
    m, success := varPointerType.MethodByName("DoSomethingWithArg")
    if success {
        m.Func.Call([]reflect.Value{
            reflect.ValueOf(pointer2obj),
            reflect.ValueOf("sad"),
        })
    }
    // 通过索引获取函数
    m = varPointerType.Method(1)
    m.Func.Call([]reflect.Value{
        reflect.ValueOf(pointer2obj),
        reflect.ValueOf("sad2"),
    })
    // 是否实现了某个接口
    fmt.Println("Implements:", varPointerType.Implements(reflect.TypeOf((*FooIF)(nil)).Elem()))
    //  看看指针多少bit
    fmt.Println("Bits: ", reflect.TypeOf(x).Bits())
    // 查看array, chan, map, ptr, slice的元素类型
    fmt.Println("Elem: ", reflect.TypeOf(simpleIntArray).Elem().Kind())
    // 查看Array长度
    fmt.Println("Len: ", reflect.TypeOf(simpleIntArray).Len())
    // 查看结构体field
    fmt.Println("Field", varType.Field(1))
    // 查看结构体field
    fmt.Println("FieldByIndex", varType.FieldByIndex([]int{2, 0}))
    // 查看结构提field
    fi, success2 := varType.FieldByName("A")
    if success2 {
        fmt.Println("FieldByName", fi)
    }
    // 查看结构体field
    fi, success2 = varType.FieldByNameFunc(func(fieldName string) bool {
        return fieldName == "A"
    })
    if success2 {
        fmt.Println("FieldByName", fi)
    }
    //  查看结构体数量
    fmt.Println("NumField", varType.NumField())
    // 查看map的key类型
    fmt.Println("Key: ", reflect.TypeOf(simpleMap).Key().Name())
    // 查看函数有多少个参数
    fmt.Println("NumIn: ", reflect.TypeOf(pointer2obj.DoSomethingWithUnCertenArg).NumIn())
    // 查看函数参数的类型
    fmt.Println("In: ", reflect.TypeOf(pointer2obj.DoSomethingWithUnCertenArg).In(0))
    // 查看最后一个参数，是否解构了
    fmt.Println("IsVariadic: ", reflect.TypeOf(pointer2obj.DoSomethingWithUnCertenArg).IsVariadic())
    // 查看函数有多少输出
    fmt.Println("NumOut: ", reflect.TypeOf(pointer2obj.DoSomethingWithUnCertenArg).NumOut())
    // 查看函数输出的类型
    fmt.Println("Out: ", reflect.TypeOf(pointer2obj.returnOneResult).Out(0))
    // 查看通道的方向, 3双向。
    fmt.Println("ChanDir: ", int(reflect.TypeOf(simpleChan).ChanDir()))
    // 查看该类型是否可以比较。不能比较的slice, map, func
    fmt.Println("Comparable: ", varPointerType.Comparable())
    // 查看类型是否可以转化成另外一种类型
    fmt.Println("ConvertibleTo: ", varPointerType.ConvertibleTo(reflect.TypeOf("a")))
    // 该类型的值是否可以另外一个类型
    fmt.Println("AssignableTo: ", reflect.TypeOf(x).AssignableTo(reflect.TypeOf(y)))
}

refVal := reflect.ValueOf(var)

refPtrVal := reflect.ValueOf(&var)

refPtrVal.Elem().Set(newRefValue)

newPtrVal := reflect.New(varType)

package main
import (
    "fmt"
    "reflect"
)
func main() {
    // swap is the implementation passed to MakeFunc.
    // It must work in terms of reflect.Values so that it is possible
    // to write code without knowing beforehand what the types
    // will be.
    swap := func(in []reflect.Value) []reflect.Value {
        return []reflect.Value{in[1], in[0]}
    }
    // makeSwap expects fptr to be a pointer to a nil function.
    // It sets that pointer to a new function created with MakeFunc.
    // When the function is invoked, reflect turns the arguments
    // into Values, calls swap, and then turns swap's result slice
    // into the values returned by the new function.
    makeSwap := func(fptr interface{}) {
        // fptr is a pointer to a function.
        // Obtain the function value itself (likely nil) as a reflect.Value
        // so that we can query its type and then set the value.
        fn := reflect.ValueOf(fptr).Elem()
        // Make a function of the right type.
        v := reflect.MakeFunc(fn.Type(), swap)
        // Assign it to the value fn represents.
        fn.Set(v)
    }
    // Make and call a swap function for ints.
    var intSwap func(int, int) (int, int)
    makeSwap(&intSwap)
    fmt.Println(intSwap(0, 1))
    // Make and call a swap function for float64s.
    var floatSwap func(float64, float64) (float64, float64)
    makeSwap(&floatSwap)
    fmt.Println(floatSwap(2.72, 3.14))
}

type MyInt int
var i int
var j MyInt

package main
import (
    "fmt"
)
type A interface {
    x(param int)
}
type B interface {
    y(param int)
}
type AB struct {
}
func (ab *AB) x(param int) {
    fmt.Printf("%p", ab)
    fmt.Println(param)
}
func (ab *AB) y(param int) {
    fmt.Printf("%p", ab)
    fmt.Println(param)
}
func printX(a A){
    fmt.Printf("%p", a)
    a.x(2)
}
func printY(b B){
    fmt.Printf("%p", b)
    b.y(3)
}
func main() {
    var ab = new(AB)
    printX(ab)
    printY(ab)
    var aInfImpl A
    var bInfImpl B
    aInfImpl = new(AB)
    //bInfImpl = aInfImpl  会报错
    bInfImpl = aInfImpl.(B)
    bInfImpl.y(2)
}

package main
import (
    "fmt"
    "reflect"
)
func main() {
    var x float64 = 3.4
    fmt.Println("type:", reflect.TypeOf(x))
}

type: float64

func TypeOf(i interface{}) Type

y := v.Interface().(float64) // y will have type float64.
fmt.Println(y)

fmt.Println(v.Interface())

fmt.Println("Value is %7.le\n", v.Interface())

var x float64 = 3.4
v := reflect.ValueOf(x)
v.SetFloat(7.1) // Error: will panic.

panic: reflect.Value.SetFloat using unaddressable value

var x float64 = 3.4
v := reflect.ValueOf(x)
fmt.Println("settability of v:", v.CanSet())