golang：采用反射的一个递归的值显示器

《GO程序设计语言》设计中案例，仅作为笔记进行收藏。反射案例。

• 值显示器的代码

package display

import (
	"fmt"
	"reflect"
	"strconv"
)

func Display(name string, x interface{}) {
	fmt.Printf("Display %s (%T):\n", name, x)
	display(name, reflect.ValueOf(x))
}

func formatAtom(v reflect.Value) string {
	switch v.Kind() {
	case reflect.Invalid:
		return "invalid"
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return strconv.FormatInt(v.Int(), 10)
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		return strconv.FormatUint(v.Uint(), 10)
	case reflect.Bool:
		if v.Bool() {
			return "true"
		}
		return "false"
	case reflect.String:
		return strconv.Quote(v.String())
	case reflect.Chan, reflect.Func, reflect.Ptr, reflect.Slice, reflect.Map:
		return v.Type().String() + " 0x" + strconv.FormatUint(uint64(v.Pointer()), 16)
	default: // reflect.Array, reflect.Struct, reflect.Interface
		return v.Type().String() + " value"
	}
}

func display(path string, v reflect.Value) {
	switch v.Kind() {
	case reflect.Invalid:
		fmt.Printf("%s = invalid\n", path)
	case reflect.Slice, reflect.Array:
		for i := 0; i < v.Len(); i++ {
			display(fmt.Sprintf("%s[%d]", path, i), v.Index(i))
		}
	case reflect.Struct:
		for i := 0; i < v.NumField(); i++ {
			fieldPath := fmt.Sprintf("%s.%s", path, v.Type().Field(i).Name)
			display(fieldPath, v.Field(i))
		}
	case reflect.Map:
		for _, key := range v.MapKeys() {
			display(fmt.Sprintf("%s[%s]", path,
				formatAtom(key)), v.MapIndex(key))
		}
	case reflect.Ptr:
		if v.IsNil() {
			fmt.Printf("%s = nil\n", path)
		} else {
			display(fmt.Sprintf("(*%s)", path), v.Elem())
		}
	case reflect.Interface:
		if v.IsNil() {
			fmt.Printf("%s = nil\n", path)
		} else {
			fmt.Printf("%s.type = %s\n", path, v.Elem().Type())
			display(path+".value", v.Elem())
		}
	default: // basic types, channels, funcs
		fmt.Printf("%s = %s\n", path, formatAtom(v))
	}
}

• 测试代码

package display

import (
	"io"
	"net"
	"os"
	"reflect"
	"sync"
	"testing"
)

func Example_slice() {
	Display("slice", []*int{new(int), nil})
	// Output:
	// Display slice ([]*int):
	// (*slice[0]) = 0
	// slice[1] = nil
}

func Example_nilInterface() {
	var w io.Writer
	Display("w", w)
	// Output:
	// Display w ():
	// w = invalid
}

func Example_ptrToInterface() {
	var w io.Writer
	Display("&w", &w)
	// Output:
	// Display &w (*io.Writer):
	// (*&w) = nil
}

func Example_struct() {
	Display("x", struct{ x interface{} }{3})
	// Output:
	// Display x (struct { x interface {} }):
	// x.x.type = int
	// x.x.value = 3
}

func Example_interface() {
	var i interface{} = 3
	Display("i", i)
	// Output:
	// Display i (int):
	// i = 3
}

func Example_ptrToInterface2() {
	var i interface{} = 3
	Display("&i", &i)
	// Output:
	// Display &i (*interface {}):
	// (*&i).type = int
	// (*&i).value = 3
}

func Example_array() {
	Display("x", [1]interface{}{3})
	// Output:
	// Display x ([1]interface {}):
	// x[0].type = int
	// x[0].value = 3
}

func Example_movie() {
	//!+movie
	type Movie struct {
		Title, Subtitle string
		Year            int
		Color           bool
		Actor           map[string]string
		Oscars          []string
		Sequel          *string
	}
	//!-movie
	//!+strangelove
	strangelove := Movie{
		Title:    "Dr. Strangelove",
		Subtitle: "How I Learned to Stop Worrying and Love the Bomb",
		Year:     1964,
		Color:    false,
		Actor: map[string]string{
			"Dr. Strangelove":            "Peter Sellers",
			"Grp. Capt. Lionel Mandrake": "Peter Sellers",
			"Pres. Merkin Muffley":       "Peter Sellers",
			"Gen. Buck Turgidson":        "George C. Scott",
			"Brig. Gen. Jack D. Ripper":  "Sterling Hayden",
			`Maj. T.J. "King" Kong`:      "Slim Pickens",
		},

		Oscars: []string{
			"Best Actor (Nomin.)",
			"Best Adapted Screenplay (Nomin.)",
			"Best Director (Nomin.)",
			"Best Picture (Nomin.)",
		},
	}
	//!-strangelove
	Display("strangelove", strangelove)

	// Output:
	// Display strangelove (display.Movie):
	// strangelove.Title = "Dr. Strangelove"
	// strangelove.Subtitle = "How I Learned to Stop Worrying and Love the Bomb"
	// strangelove.Year = 1964
	// strangelove.Color = false
	// strangelove.Actor["Gen. Buck Turgidson"] = "George C. Scott"
	// strangelove.Actor["Brig. Gen. Jack D. Ripper"] = "Sterling Hayden"
	// strangelove.Actor["Maj. T.J. \"King\" Kong"] = "Slim Pickens"
	// strangelove.Actor["Dr. Strangelove"] = "Peter Sellers"
	// strangelove.Actor["Grp. Capt. Lionel Mandrake"] = "Peter Sellers"
	// strangelove.Actor["Pres. Merkin Muffley"] = "Peter Sellers"
	// strangelove.Oscars[0] = "Best Actor (Nomin.)"
	// strangelove.Oscars[1] = "Best Adapted Screenplay (Nomin.)"
	// strangelove.Oscars[2] = "Best Director (Nomin.)"
	// strangelove.Oscars[3] = "Best Picture (Nomin.)"
	// strangelove.Sequel = nil
}

func Test(t *testing.T) {
	// Some other values (YMMV)
	Display("os.Stderr", os.Stderr)
	// Output:
	// Display os.Stderr (*os.File):
	// (*(*os.Stderr).file).fd = 2
	// (*(*os.Stderr).file).name = "/dev/stderr"
	// (*(*os.Stderr).file).nepipe = 0

	var w io.Writer = os.Stderr
	Display("&w", &w)
	// Output:
	// Display &w (*io.Writer):
	// (*&w).type = *os.File
	// (*(*(*&w).value).file).fd = 2
	// (*(*(*&w).value).file).name = "/dev/stderr"
	// (*(*(*&w).value).file).nepipe = 0

	var locker sync.Locker = new(sync.Mutex)
	Display("(&locker)", &locker)
	// Output:
	// Display (&locker) (*sync.Locker):
	// (*(&locker)).type = *sync.Mutex
	// (*(*(&locker)).value).state = 0
	// (*(*(&locker)).value).sema = 0

	Display("locker", locker)
	// Output:
	// Display locker (*sync.Mutex):
	// (*locker).state = 0
	// (*locker).sema = 0
	// (*(&locker)) = nil

	locker = nil
	Display("(&locker)", &locker)
	// Output:
	// Display (&locker) (*sync.Locker):
	// (*(&locker)) = nil

	ips, _ := net.LookupHost("golang.org")
	Display("ips", ips)
	// Output:
	// Display ips ([]string):
	// ips[0] = "173.194.68.141"
	// ips[1] = "2607:f8b0:400d:c06::8d"

	Display("rV", reflect.ValueOf(os.Stderr))
	// Output:
	// Display rV (reflect.Value):
	// (*rV.typ).size = 8
	// (*rV.typ).ptrdata = 8
	// (*rV.typ).hash = 871609668
	// (*rV.typ)._ = 0

	// a pointer that points to itself
	type P *P
	var p P
	p = &p
	if false {
		Display("p", p)
		// Output:
		// Display p (display.P):
	}

	// a map that contains itself
	type M map[string]M
	m := make(M)
	m[""] = m
	if false {
		Display("m", m)
		// Output:
		// Display m (display.M):
	}

	// a slice that contains itself
	type S []S
	s := make(S, 1)
	s[0] = s
	if false {
		Display("s", s)
		// Output:
		// Display s (display.S):
	}

	// a linked list that eats its own tail
	type Cycle struct {
		Value int
		Tail  *Cycle
	}
	var c Cycle
	c = Cycle{42, &c}
	if false {
		Display("c", c)
		// Output:
		// Display c (display.Cycle):
		// c.Value = 42
		// (*c.Tail).Value = 42
		// (*(*c.Tail).Tail).Value = 42
	}
}