调用以指针作为接收者的指针的方法表达式

Question

There is func someFunc(v interface{}, fn interface{}) where v is a pointer to struct (say *A) and fn is a method expression (say (*A).method()). How to call fn with v as parameter (using reflect)?

Answer 1

It's possible to do with reflect.Value.Call(), however it's pretty cumbersome, especially if you need to do something with the return value. But here's a basic example:

package main

import (
    "fmt"
    "reflect"
)

type Foo struct {
    Bar string
}

func concrete(foo *Foo) {
    fmt.Printf("Foo: %#v
", foo)
}

func someFunc(v interface{}, fn interface{}) {

    f := reflect.ValueOf(fn)
    arg := reflect.ValueOf(v)

    f.Call([]reflect.Value{arg})
}

func main() {
    foo := Foo{"Bar"}
    someFunc(&foo, concrete)

}

// Output: Foo: &main.Foo{Bar:"Bar"}

https://play.golang.org/p/ED6QdvENxti

If you want to call a method of a struct by name, we need to revise it just a bit:

type Foo struct {
    Bar string
}

func (f *Foo) Concrete() {
    fmt.Printf("Foo: %#v
", f)
}

func callByName(v interface{}, fn string) {
    arg := reflect.ValueOf(v)
    f := arg.MethodByName(fn)
    f.Call([]reflect.Value{})
}

func main() {
    foo := Foo{"Bar"}
    callByName(&foo, "Concrete")

}

Notice that in this case the method value is already bound to the struct instance, so we don't need to pass it anything as an argument.