deco.go

package main

import (
	"fmt"
	"reflect"
	"runtime"
)

func Decorator(decoPtr, fn interface{}) (err error) {
	var decoratedFunc, targetFunc reflect.Value

	decoratedFunc = reflect.ValueOf(decoPtr).Elem()
	targetFunc = reflect.ValueOf(fn)
	var funcName = runtime.FuncForPC(reflect.ValueOf(fn).Pointer()).Name()
	v := reflect.MakeFunc(targetFunc.Type(),
		func(in []reflect.Value) (out []reflect.Value) {
			// fmt.Println("before")
			out = targetFunc.Call(in)
			fmt.Println("funcName", funcName)
			fmt.Println("args", in)
			// fmt.Println("after")
			return
		})

	decoratedFunc.Set(v)
	return
}

func bar(a, b string) string {
	return a + b
}

func main() {
	mybar := bar
	Decorator(&mybar, bar)
	mybar("hello,", "world!")
}