doc: add The Laws of Reflection article
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
diff --git a/doc/progs/interface2.go b/doc/progs/interface2.go
new file mode 100644
index 0000000..e2716cf
--- /dev/null
+++ b/doc/progs/interface2.go
@@ -0,0 +1,112 @@
+package main
+
+import (
+ "fmt"
+ "reflect"
+)
+
+func main() {
+ var x float64 = 3.4
+ fmt.Println("type:", reflect.TypeOf(x))
+ // STOP OMIT
+ // TODO(proppy): test output OMIT
+}
+
+// STOP main OMIT
+
+func f1() {
+ // START f1 OMIT
+ var x float64 = 3.4
+ v := reflect.ValueOf(x)
+ fmt.Println("type:", v.Type())
+ fmt.Println("kind is float64:", v.Kind() == reflect.Float64)
+ fmt.Println("value:", v.Float())
+ // STOP OMIT
+}
+
+func f2() {
+ // START f2 OMIT
+ var x uint8 = 'x'
+ v := reflect.ValueOf(x)
+ fmt.Println("type:", v.Type()) // uint8.
+ fmt.Println("kind is uint8: ", v.Kind() == reflect.Uint8) // true.
+ x = uint8(v.Uint()) // v.Uint returns a uint64.
+ // STOP OMIT
+}
+
+func f3() {
+ // START f3 OMIT
+ type MyInt int
+ var x MyInt = 7
+ v := reflect.ValueOf(x)
+ // START f3b OMIT
+ y := v.Interface().(float64) // y will have type float64.
+ fmt.Println(y)
+ // START f3c OMIT
+ fmt.Println(v.Interface())
+ // START f3d OMIT
+ fmt.Printf("value is %7.1e\n", v.Interface())
+ // STOP OMIT
+}
+
+func f4() {
+ // START f4 OMIT
+ var x float64 = 3.4
+ v := reflect.ValueOf(x)
+ v.SetFloat(7.1) // Error: will panic.
+ // STOP OMIT
+}
+
+func f5() {
+ // START f5 OMIT
+ var x float64 = 3.4
+ v := reflect.ValueOf(x)
+ fmt.Println("settability of v:", v.CanSet())
+ // STOP OMIT
+}
+
+func f6() {
+ // START f6 OMIT
+ var x float64 = 3.4
+ v := reflect.ValueOf(x)
+ // START f6b OMIT
+ v.SetFloat(7.1)
+ // STOP OMIT
+}
+
+func f7() {
+ // START f7 OMIT
+ var x float64 = 3.4
+ p := reflect.ValueOf(&x) // Note: take the address of x.
+ fmt.Println("type of p:", p.Type())
+ fmt.Println("settability of p:", p.CanSet())
+ // START f7b OMIT
+ v := p.Elem()
+ fmt.Println("settability of v:", v.CanSet())
+ // START f7c OMIT
+ v.SetFloat(7.1)
+ fmt.Println(v.Interface())
+ fmt.Println(x)
+ // STOP OMIT
+}
+
+func f8() {
+ // START f8 OMIT
+ type T struct {
+ A int
+ B string
+ }
+ 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", i,
+ typeOfT.Field(i).Name, f.Type(), f.Interface())
+ }
+ // START f8b OMIT
+ s.Field(0).SetInt(77)
+ s.Field(1).SetString("Sunset Strip")
+ fmt.Println("t is now", t)
+ // STOP OMIT
+}
