Go反射编程
reflect.TypeOf vs. reflect.ValueOf：
- reflflect.TypeOf 返回类型 (reflflect.Type)
- reflflect.ValueOf 返回值 (reflflect.Value)
- 可以从 reflflect.Value 获得类型
- 通过 kind 的来判断类型
func CheckType(v interface{}) {
t := reflect.TypeOf(v)
switch t.Kind() {
case reflect.Float32, reflect.Float64:
fmt.Println("Float")
case reflect.Int, reflect.Int32, reflect.Int64:
fmt.Println("Integer")
default:
fmt.Println("Unknown", t)
}
}
func TestBasicType(t *testing.T) {
var f float64 = 12
CheckType(f)
/** 运行结果：
=== RUN TestBasicType
Float
--- PASS: TestBasicType (0.00s)
*/
}
利用反射编写灵活的代码：
-
按名字访问结构的成员
reflect.ValueOf(*e).FieldByName("Name") -
按名字访问结构的方法
reflect.ValueOf(*e).MethodByName("UpdateAge").Call([]reflect.Value{reflect.ValueOf(1)})
type Employee struct {
EmployeeId string
Name string `format:"normal"`
Age int
}
func (e *Employee) UpdateAge(newVal int) {
e.Age = newVal
}
func TestInvokeByName(t *testing.T) {
e := &Employee{"1", "Mike", 30}
// 按名字获取成员
t.Logf("Name：value(%[1]v)，Type(%[1]T)", reflect.ValueOf(*e).FieldByName("Name"))
if nameField, ok := reflect.TypeOf(*e).FieldByName("Name"); !ok {
t.Error("Failed to get 'Name' field.")
} else {
t.Log("Tag:format", nameField.Tag.Get("format"))
}
reflect.ValueOf(e).MethodByName("UpdateAge").Call([]reflect.Value{reflect.ValueOf(1)})
t.Log("Updated Age:", e)
/** 运行结果：
=== RUN TestInvokeByName
TestInvokeByName: reflect_test.go:28: Name：value(Mike)，Type(reflect.Value)
TestInvokeByName: reflect_test.go:32: Tag:format normal
TestInvokeByName: reflect_test.go:35: Updated Age: &{1 Mike 1}
--- PASS: TestInvokeByName (0.00s)
*/
}
Struct Tag：
type BasicInfo struct {
Name string `json:"name"`
Age int `json:"age"`
}
访问Struct：
if nameField, ok := reflect.TypeOf(*e).FieldByName("Name"); !ok {
t.Error("Failed to get 'Name' field.")
} else {
t.Log("Tag:format", nameField.Tag.Get("format")) }
Reflect.Type 和 Reflflect.Value 都有 FieldByName ⽅法，注意他们的区别。
DeepEqual：
比较切片和map
type Customer struct {
CookieID string
Name string
Age int
}
func TestDeepEqual(t *testing.T) {
a := map[int]string{1: "one", 2: "two", 3: "three"}
b := map[int]string{1: "one", 2: "two", 4: "three"}
fmt.Println(reflect.DeepEqual(a, b))
s1 := []int{1, 2, 3}
s2 := []int{1, 2, 3}
s3 := []int{2, 3, 1}
t.Log("s1 == s2?", reflect.DeepEqual(s1, s2))
t.Log("s1 == s3?", reflect.DeepEqual(s1, s3))
c1 := Customer{"1", "Mike", 40}
c2 := Customer{"1", "Mike", 40}
fmt.Println(reflect.DeepEqual(c1, c2))
/** 运行结果：
=== RUN TestDeepEqual
false
TestDeepEqual: fiexible_reflect_test.go:23: s1 == s2? true
TestDeepEqual: fiexible_reflect_test.go:24: s1 == s3? false
true
--- PASS: TestDeepEqual (0.00s)
*/
}
关于“反射”你应该知道的：
-
提⾼了程序的灵活性
-
降低了程序的可读性
-
降低了程序的性能
type Employee struct {
EmployeeID string
Name string `format:"normal"`
Age int
}
func (e *Employee) UpdateAge(newVal int) {
e.Age = newVal
}
type Customer struct {
CookieID string
Name string
Age int
}
func fillBySettings(st interface{}, settings map[string]interface{}) error {
// func (v Value) Elem() Value
// Elem returns the value that the interface v contains or that the pointer v points to.
// It panics if v's Kind is not Interface or Ptr.
// It returns the zero Value if v is nil.
if reflect.TypeOf(st).Kind() != reflect.Ptr {
return errors.New("the first param should be a pointer to the struct type.")
}
// Elem() 获取指针指向的值
if reflect.TypeOf(st).Elem().Kind() != reflect.Struct {
return errors.New("the first param should be a pointer to the struct type.")
}
if settings == nil {
return errors.New("settings is nil.")
}
var (
field reflect.StructField
ok bool
)
for k, v := range settings {
if field, ok = (reflect.ValueOf(st)).Elem().Type().FieldByName(k); !ok {
continue
}
if field.Type == reflect.TypeOf(v) {
vstr := reflect.ValueOf(st)
vstr = vstr.Elem()
vstr.FieldByName(k).Set(reflect.ValueOf(v))
}
}
return nil
}
func TestFillNameAndAge(t *testing.T) {
settings := map[string]interface{}{"Name": "Mike", "Age": 30}
e := Employee{}
if err := fillBySettings(&e, settings); err != nil {
t.Fatal(err)
}
t.Log(e)
c := new(Customer)
if err := fillBySettings(c, settings); err != nil {
t.Fatal(err)
}
t.Log(*c)
/** 运行结果：
=== RUN TestFillNameAndAge
TestFillNameAndAge: fiexible_reflect_test.go:69: { Mike 30}
TestFillNameAndAge: fiexible_reflect_test.go:74: { Mike 30}
--- PASS: TestFillNameAndAge (0.00s)
*/
}
”不安全“行为的危险性：
func TestUnsafe(t *testing.T) {
i := 10
f := *(*float64)(unsafe.Pointer(&i))
t.Log(unsafe.Pointer(&i))
t.Log(f)
/** 运行结果：
=== RUN TestUnsafe
TestUnsafe: unsafe_test.go:11: 0xc000016268
TestUnsafe: unsafe_test.go:12: 5e-323
--- PASS: TestUnsafe (0.00s)
*/
}
// The cases is suitable for unsafe
type MyInt int
// 合理的类型转换
func TestConvert(t *testing.T) {
a := []int{1, 2, 3, 4}
b := *(*[]MyInt)(unsafe.Pointer(&a))
t.Log(b)
/** 运行结果：
=== RUN TestConvert
TestConvert: unsafe_test.go:26: [1 2 3 4]
--- PASS: TestConvert (0.00s)
*/
}
// 原子类型操作
func TestAtomic(t *testing.T) {
var shareBuffer unsafe.Pointer
writeDataFn := func() {
data := []int{}
for i := 0; i < 100; i++ {
data = append(data, i)
}
atomic.StorePointer(&shareBuffer, unsafe.Pointer(&data))
}
readDataFn := func() {
data := atomic.LoadPointer(&shareBuffer)
fmt.Println(data, *(*[]int)(data))
}
var wg sync.WaitGroup
writeDataFn()
for i := 0; i < 10; i++ {
wg.Add(1)
go func() {
for i := 0; i < 10; i++ {
writeDataFn()
time.Sleep(time.Microsecond * 100)
}
wg.Done()
}()
wg.Add(1)
go func() {
for i := 0; i < 10; i++ {
readDataFn()
time.Sleep(time.Microsecond * 100)
}
wg.Done()
}()
}
wg.Wait()
}