func.go

package main

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

/**
函数返回多个值时可以起名字
仅用于非常简单的函数
对于调用者而言没有区别

返回值类型写在最后面
可返回多个值
函数作为参数
没有默认参数，可选参数
 */
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 "/":
		q, _ := div(a, b)
		return q, nil
	default:
		return 0, fmt.Errorf("UnsupportedError:%s", op)
	}
}

func div(a, b int) (q, r int) {
	return a / b, a % b
}

func apply(op func(int, int) int, a, b int) int {
	p := reflect.ValueOf(op).Pointer()
	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 swap(a, b *int) {
	*b, *a = *a, *b
}

func swap2(a, b int) (int, int) {
	return b, a
}

func main() {

	if result, err := eval(3, 4, "/"); err != nil {
		fmt.Println("Error:", err)
	} else {
		fmt.Println(result)
	}

	q, r := div(13, 3)
	fmt.Println(q, r)

	fmt.Println(apply(pow, 3, 5))

	fmt.Println(apply(func(a int, b int) int {
		return int(math.Pow(float64(a), float64(b)))
	}, 3, 5))

	fmt.Println(sum(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))

	a, b := 3, 4
	swap(&a, &b)
	fmt.Println(a, b)
	a, b = swap2(a, b)
	fmt.Println(a, b)
}