package main

import (

	"fmt"

	"reflect"

	"runtime"

	"math"

)

func eval(a,b int, op string) (int,error){

	switch op{

	case "+":

		return a+b,nil

	case "-":

		return a-b,nil

	case "*":

		return a*b,nil

	case "/":

		//result = a/b

		//两个返回值中取其中一个返回值

		q,_ :=div(a,b)

		return q,nil

	default:

		return 0,fmt.Errorf(

			"unsupported operation %s	",op,

		)

	}

}

//返回多个值

func div(a,b int) (q,r int){

	//q = a / b

	//r = a % b

	//return

	return a / b, a % b

}

//函数里面的参数可以时函数

func apply(op func(int, int) int,  a, b int) int {

	p:=reflect.ValueOf(op).Pointer()//获取函数的指针

	opName:=runtime.FuncForPC(p).Name()

	fmt.Printf("Calling function %s with args" +

	"(%d,%d)\n",opName,a,b)

	return op(a,b)

}

func pow(a,b int) int {

	return  int(math.Pow(float64(a),float64(b)))

}

func sum(numbers ...int) int{

	s := 0

	for i := range numbers{

		s += numbers[i]

	}

	return s

}

func main() {

	//fmt.Println(

	//	eval(3,4,"x"),

	//)

	//q,r :=div(13,3)

	//fmt.Println(q,r)

	fmt.Println(apply(func(a int, b int) int {

		return int(math.Pow(float64(a),float64(b)))

	},3,4))

	fmt.Println(apply(pow,3,4))

	fmt.Println(sum(1,2,3,4,5))

}

package main

import "fmt"

func main() {

	var f = Adder()

	fmt.Print(f(1), " - ")

	fmt.Print(f(20), " - ")

	fmt.Print(f(300))

}

func Adder() func(int) int {

	var x int

	return func(delta int) int {

		x += delta

		return x

	}

}

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