reflect: add example for StructOf

This CL adds a simple example for StructOf.
The example shows how StructOf can be used in a JSON roundtrip.

Change-Id: I9ff1ea9cb8c0cf297c5fae74e68b89931076adfd
Reviewed-on: https://go-review.googlesource.com/33953
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/reflect/example_test.go

@@ -5,6 +5,8 @@
 package reflect_test
 
 import (
+	"bytes"
+	"encoding/json"
 	"fmt"
 	"io"
 	"os"
@@ -107,3 +109,42 @@ func ExampleTypeOf() {
 	// Output:
 	// true
 }
+
+func ExampleStructOf() {
+	typ := reflect.StructOf([]reflect.StructField{
+		{
+			Name: "Height",
+			Type: reflect.TypeOf(float64(0)),
+			Tag:  `json:"height"`,
+		},
+		{
+			Name: "Age",
+			Type: reflect.TypeOf(int(0)),
+			Tag:  `json:"age"`,
+		},
+	})
+
+	v := reflect.New(typ).Elem()
+	v.Field(0).SetFloat(0.4)
+	v.Field(1).SetInt(2)
+	s := v.Addr().Interface()
+
+	w := new(bytes.Buffer)
+	if err := json.NewEncoder(w).Encode(s); err != nil {
+		panic(err)
+	}
+
+	fmt.Printf("value: %+v\n", s)
+	fmt.Printf("json:  %s", w.Bytes())
+
+	r := bytes.NewReader([]byte(`{"height":1.5,"age":10}`))
+	if err := json.NewDecoder(r).Decode(s); err != nil {
+		panic(err)
+	}
+	fmt.Printf("value: %+v\n", s)
+
+	// Output:
+	// value: &{Height:0.4 Age:2}
+	// json:  {"height":0.4,"age":2}
+	// value: &{Height:1.5 Age:10}
+}