如何使用反射调用带有指针接收器的结构上的方法？

Question

I am working with reflection in Go and have some issues trying to call a method on a struct that has a pointer receiver. I have the following go code:

package main

import (
    "fmt"
    "reflect"
)

type Base struct {
    Name     string
    Greeting string
}

func (b *Base) SetGreeting() {
    b.Greeting = fmt.Sprintf("Hello %s\n", b.Name)
}

func main() {
    var pointer interface{}

    // create a new instance of base
    mybase := Base{
        Name: "reflect",
    }

    // create a pointer to the base
    pointer = &mybase

    s := reflect.ValueOf(pointer).Elem()

    // get the value of s which should be a pointer
    vv := reflect.ValueOf(s)
    switch vv.Kind() {
    case reflect.Struct:
        fmt.Println("struct")
    case reflect.Ptr:
        fmt.Println("pointer")
    }

    // output struct property
    fmt.Println(s.FieldByName("Name").String())

    // call the method using reflect
    sayHelloFunc := s.MethodByName("SetGreeting")

    if sayHelloFunc.IsValid() {
        sayHelloFunc.Call([]reflect.Value{})
    } else {
        fmt.Println("Unable to find method")
    }

    fmt.Println(s.FieldByName("Greeting").String())
}

The above is available at https://play.golang.org/p/V04m3LJlRia

If I change the method to use a value receiver then the method works, but I am not able to get the Greeting property. If use the pointer receiver (as in the code) the method cannot be found but I can access the property.

How can I do both?

Answer 1

Thanks to @Volker this is now working. The slightly modified code is:

package main

import (
    "fmt"
    "reflect"
)

type Base struct {
    Name     string
    Greeting string
}

func (b *Base) SetGreeting() {
    b.Greeting = fmt.Sprintf("Hello %s\n", b.Name)
}

func main() {
    var pointer interface{}

    // create a new instance of base
    mybase := Base{
        Name: "reflect",
    }

    // create a pointer to the base
    pointer = &mybase

    s := reflect.ValueOf(pointer)

    // get the value of s which should be a pointer
    vv := reflect.ValueOf(s)
    switch vv.Kind() {
    case reflect.Struct:
        fmt.Println("struct")
    case reflect.Ptr:
        fmt.Println("pointer")
    }

    // output struct property
    fmt.Println(s.Elem().FieldByName("Name").String())

    // call the method using reflect
    sayHelloFunc := s.MethodByName("SetGreeting")

    if sayHelloFunc.IsValid() {
        sayHelloFunc.Call([]reflect.Value{})
    } else {
        fmt.Println("Unable to find method")
    }

    fmt.Println(s.Elem().FieldByName("Greeting").String())
}

As can be seen s is no longer set as a pointer and the method can be called.

As I wanted to be able to call the properties on s I then make it a pointer using .Elem() and then I can use FieldByName .

Updated here https://play.golang.org/p/iiUrB961tUa