Initial commit: Go 1.23 release state

src/reflect/example_test.go

@@ -0,0 +1,209 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package reflect_test
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"os"
+	"reflect"
+)
+
+func ExampleKind() {
+	for _, v := range []any{"hi", 42, func() {}} {
+		switch v := reflect.ValueOf(v); v.Kind() {
+		case reflect.String:
+			fmt.Println(v.String())
+		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+			fmt.Println(v.Int())
+		default:
+			fmt.Printf("unhandled kind %s", v.Kind())
+		}
+	}
+
+	// Output:
+	// hi
+	// 42
+	// unhandled kind func
+}
+
+func ExampleMakeFunc() {
+	// 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 any) {
+		// 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))
+
+	// Output:
+	// 1 0
+	// 3.14 2.72
+}
+
+func ExampleStructTag() {
+	type S struct {
+		F string `species:"gopher" color:"blue"`
+	}
+
+	s := S{}
+	st := reflect.TypeOf(s)
+	field := st.Field(0)
+	fmt.Println(field.Tag.Get("color"), field.Tag.Get("species"))
+
+	// Output:
+	// blue gopher
+}
+
+func ExampleStructTag_Lookup() {
+	type S struct {
+		F0 string `alias:"field_0"`
+		F1 string `alias:""`
+		F2 string
+	}
+
+	s := S{}
+	st := reflect.TypeOf(s)
+	for i := 0; i < st.NumField(); i++ {
+		field := st.Field(i)
+		if alias, ok := field.Tag.Lookup("alias"); ok {
+			if alias == "" {
+				fmt.Println("(blank)")
+			} else {
+				fmt.Println(alias)
+			}
+		} else {
+			fmt.Println("(not specified)")
+		}
+	}
+
+	// Output:
+	// field_0
+	// (blank)
+	// (not specified)
+}
+
+func ExampleTypeOf() {
+	// As interface types are only used for static typing, a
+	// common idiom to find the reflection Type for an interface
+	// type Foo is to use a *Foo value.
+	writerType := reflect.TypeOf((*io.Writer)(nil)).Elem()
+
+	fileType := reflect.TypeOf((*os.File)(nil))
+	fmt.Println(fileType.Implements(writerType))
+
+	// 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}
+}
+
+func ExampleValue_FieldByIndex() {
+	// This example shows a case in which the name of a promoted field
+	// is hidden by another field: FieldByName will not work, so
+	// FieldByIndex must be used instead.
+	type user struct {
+		firstName string
+		lastName  string
+	}
+
+	type data struct {
+		user
+		firstName string
+		lastName  string
+	}
+
+	u := data{
+		user:      user{"Embedded John", "Embedded Doe"},
+		firstName: "John",
+		lastName:  "Doe",
+	}
+
+	s := reflect.ValueOf(u).FieldByIndex([]int{0, 1})
+	fmt.Println("embedded last name:", s)
+
+	// Output:
+	// embedded last name: Embedded Doe
+}
+
+func ExampleValue_FieldByName() {
+	type user struct {
+		firstName string
+		lastName  string
+	}
+	u := user{firstName: "John", lastName: "Doe"}
+	s := reflect.ValueOf(u)
+
+	fmt.Println("Name:", s.FieldByName("firstName"))
+	// Output:
+	// Name: John
+}