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Originally published on The Go Programming Language Blog, September 6, 2011. http://blog.golang.org/2011/09/laws-of-reflection.html Update #2547 R=golang-dev, r, adg CC=golang-dev https://golang.org/cl/5689054
113 lines
2.2 KiB
Go
113 lines
2.2 KiB
Go
package main
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import (
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"fmt"
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"reflect"
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)
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func main() {
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var x float64 = 3.4
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fmt.Println("type:", reflect.TypeOf(x))
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// STOP OMIT
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// TODO(proppy): test output OMIT
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}
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// STOP main OMIT
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func f1() {
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// START f1 OMIT
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var x float64 = 3.4
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v := reflect.ValueOf(x)
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fmt.Println("type:", v.Type())
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fmt.Println("kind is float64:", v.Kind() == reflect.Float64)
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fmt.Println("value:", v.Float())
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// STOP OMIT
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}
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func f2() {
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// START f2 OMIT
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var x uint8 = 'x'
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v := reflect.ValueOf(x)
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fmt.Println("type:", v.Type()) // uint8.
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fmt.Println("kind is uint8: ", v.Kind() == reflect.Uint8) // true.
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x = uint8(v.Uint()) // v.Uint returns a uint64.
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// STOP OMIT
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}
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func f3() {
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// START f3 OMIT
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type MyInt int
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var x MyInt = 7
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v := reflect.ValueOf(x)
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// START f3b OMIT
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y := v.Interface().(float64) // y will have type float64.
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fmt.Println(y)
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// START f3c OMIT
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fmt.Println(v.Interface())
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// START f3d OMIT
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fmt.Printf("value is %7.1e\n", v.Interface())
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// STOP OMIT
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}
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func f4() {
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// START f4 OMIT
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var x float64 = 3.4
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v := reflect.ValueOf(x)
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v.SetFloat(7.1) // Error: will panic.
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// STOP OMIT
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}
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func f5() {
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// START f5 OMIT
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var x float64 = 3.4
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v := reflect.ValueOf(x)
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fmt.Println("settability of v:", v.CanSet())
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// STOP OMIT
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}
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func f6() {
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// START f6 OMIT
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var x float64 = 3.4
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v := reflect.ValueOf(x)
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// START f6b OMIT
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v.SetFloat(7.1)
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// STOP OMIT
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}
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func f7() {
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// START f7 OMIT
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var x float64 = 3.4
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p := reflect.ValueOf(&x) // Note: take the address of x.
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fmt.Println("type of p:", p.Type())
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fmt.Println("settability of p:", p.CanSet())
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// START f7b OMIT
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v := p.Elem()
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fmt.Println("settability of v:", v.CanSet())
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// START f7c OMIT
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v.SetFloat(7.1)
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fmt.Println(v.Interface())
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fmt.Println(x)
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// STOP OMIT
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}
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func f8() {
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// START f8 OMIT
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type T struct {
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A int
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B string
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}
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t := T{23, "skidoo"}
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s := reflect.ValueOf(&t).Elem()
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typeOfT := s.Type()
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for i := 0; i < s.NumField(); i++ {
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f := s.Field(i)
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fmt.Printf("%d: %s %s = %v\n", i,
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typeOfT.Field(i).Name, f.Type(), f.Interface())
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}
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// START f8b OMIT
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s.Field(0).SetInt(77)
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s.Field(1).SetString("Sunset Strip")
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fmt.Println("t is now", t)
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// STOP OMIT
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}
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