英文:
Reflection type does not have method
问题
我正在使用Go语言中的反射。为什么这段代码没有列出方法？它只列出了字段。
问题出在这里吗？value interface{} 我不确定如何将一个通用的结构体/类/类型传递给函数。通常我只会传递一个对象。
（我完全是新手。我是一名C#程序员）
package main
import (
"fmt"
"reflect"
)
func main() {
var B TestType = TestType{TestString: "Hello", TestNumber: 3}
ListMethods(B)
}
func ListMethods(value interface{}) {
fooType := reflect.TypeOf(value)
for i := 0; i < fooType.NumMethod(); i++ {
method := fooType.Method(i)
fmt.Println("Method = " + method.Name)
}
for i := 0; i < fooType.NumField(); i++ {
field := fooType.Field(i)
fmt.Println("Field = " + field.Name)
fmt.Println(reflect.ValueOf(value).Field(i))
}
}
type TestType struct {
TestString string
TestNumber int
}
func (this *TestType) TestFunction() {
fmt.Println("Test")
}
这段代码没有列出方法，是因为你的TestFunction方法是一个指针接收器方法，而你传递给ListMethods函数的值是一个值类型。要解决这个问题，你可以将ListMethods函数的参数类型改为指针类型，或者将TestType的实例化改为指针类型。
以下是修改后的代码：
package main
import (
"fmt"
"reflect"
)
func main() {
var B TestType = TestType{TestString: "Hello", TestNumber: 3}
ListMethods(&B)
}
func ListMethods(value interface{}) {
fooType := reflect.TypeOf(value)
for i := 0; i < fooType.NumMethod(); i++ {
method := fooType.Method(i)
fmt.Println("Method = " + method.Name)
}
for i := 0; i < fooType.NumField(); i++ {
field := fooType.Field(i)
fmt.Println("Field = " + field.Name)
fmt.Println(reflect.ValueOf(value).Field(i))
}
}
type TestType struct {
TestString string
TestNumber int
}
func (this *TestType) TestFunction() {
fmt.Println("Test")
}
这样修改后，你应该能够正确地列出TestType的方法。
英文:
I'm trying to use reflection in Go. Why doesn't this code list the methods? It lists the fields.
is this the problem? value interface{} I'm not sure how to pass a generic struct/class/type to a function. Normally I would just pass an Object.
(I'm totally new at this. I'm a C# programmer)
package main
import (
"fmt"
"reflect"
)
func main() {
var B TestType = TestType{TestString: "Hello", TestNumber: 3}
ListMethods(B)
}
func ListMethods(value interface{}) {
fooType := reflect.TypeOf(value)
for i := 0; i < fooType.NumMethod(); i++ {
method := fooType.Method(i)
fmt.Println("Method = " + method.Name)
}
for i := 0; i < fooType.NumField(); i++ {
field := fooType.Field(i)
fmt.Println("Field = " + field.Name)
fmt.Println(reflect.ValueOf(value).Field(i))
}
}
type TestType struct {
TestString string
TestNumber int
}
func (this *TestType) TestFunction() {
fmt.Println("Test")
}
答案1
得分: 3
因为你传递了一个类型，并声明了一个方法来操作该类型的指针。
请看一下这个扩展自你的示例的例子：
package main
import (
"fmt"
"reflect"
)
func main() {
var B TestType = TestType{TestString: "Hello", TestNumber: 3}
ListMethods(B)
}
func ListMethods(value interface{}) {
fooType := reflect.TypeOf(value)
ptrFooType := reflect.PtrTo(fooType)
for i := 0; i < fooType.NumMethod(); i++ {
method := fooType.Method(i)
fmt.Println("Method = " + method.Name)
}
for i := 0; i < ptrFooType.NumMethod(); i++ {
method := ptrFooType.Method(i)
fmt.Println("* Method = " + method.Name)
}
for i := 0; i < fooType.NumField(); i++ {
field := fooType.Field(i)
fmt.Println("Field = " + field.Name)
fmt.Println(reflect.ValueOf(value).Field(i))
}
}
type TestType struct {
TestString string
TestNumber int
}
func (this *TestType) TestFunctionPtr() {
fmt.Println("Test")
}
func (this TestType) TestFunction() {
fmt.Println("Test Non Ptr")
}
注意，*Type 可以访问 Type 的方法，但 Type 无法访问 *Type 的方法。
要将 Type 转换为 *Type，我使用了 reflect.PtrTo(Type)。
英文:
Because you are passing a type and you declared a method to the pointer of the type.
https://play.golang.org/p/B0NdVyxGxt
Look at this example extended from yours:
package main
import (
"fmt"
"reflect"
)
func main() {
var B TestType = TestType{TestString: "Hello", TestNumber: 3}
ListMethods(B)
}
func ListMethods(value interface{}) {
fooType := reflect.TypeOf(value)
ptrFooType := reflect.PtrTo(fooType)
for i := 0; i < fooType.NumMethod(); i++ {
method := fooType.Method(i)
fmt.Println("Method = " + method.Name)
}
for i := 0; i < ptrFooType.NumMethod(); i++ {
method := ptrFooType.Method(i)
fmt.Println("* Method = " + method.Name)
}
for i := 0; i < fooType.NumField(); i++ {
field := fooType.Field(i)
fmt.Println("Field = " + field.Name)
fmt.Println(reflect.ValueOf(value).Field(i))
}
}
type TestType struct {
TestString string
TestNumber int
}
func (this *TestType) TestFunctionPtr() {
fmt.Println("Test")
}
func (this TestType) TestFunction() {
fmt.Println("Test Non Ptr")
}
Notice how the *Type can access also the Type Methods. But Type cannot access to *Type Methods.
To convert from Type to *Type I have used the reflect.PtrTo(Type).
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