go - 如何使用反射从另一个函数创建新函数

Question

使用此代码作为模板

package main

import "fmt"

type myStruct struct {
    Value int
}

type counter int

func newFuncHandler(fn func(myStruct) error) (interface{}, *counter) {
    count := counter(0)

    newFn := func(e myStruct) error {
        count = count + 1
        return fn(e)
    }

    return newFn, &count
}

func main() {
    fn := func(d myStruct) error {
        // doing some stuff
        return nil
    }

    handle, c := newFuncHandler(fn)
    handleFn := handle.(func(d myStruct) error)

    handleFn(myStruct{Value: 2})
    handleFn(myStruct{Value: 2})
    handleFn(myStruct{Value: 2})
    handleFn(myStruct{Value: 2})
    handleFn(myStruct{Value: 2})

    fmt.Println(*c) // 5
}

如何修改newFuncHandler，以使其在给定具有未知签名的函数的情况下返回具有相同签名但为函数主体提供附加代码的函数。 newFuncHandler不应该知道myStruct类型

例如

func newFuncHandler(fn interface{}) (interface{}, *counter) {
    count := counter(0)
    // some reflection magic

    // newFn has the same signature as fn (hardcoded in this case)
    newFn := func(e myStruct) error {
        // add custom code 
        count = count + 1

        // call the original fn
        return fn(e)
    }

    return newFn, &count
}

Answer 1

使用reflect.MakeFunc进行功能。使用Value.Call调用函数。

func newFuncHandler(v interface{}) (interface{}, *counter) {
    count := counter(0)
    fn := reflect.ValueOf(v)
    newFn := reflect.MakeFunc(fn.Type(), func(args []reflect.Value) (results []reflect.Value) {
        count = count + 1
        return fn.Call(args)
    })
    return newFn.Interface(), &count
}

Run it on the playground。