Go學習：切片slice的循環機制及性能

使用range來循環切片時，每一輪都會向同一個臨時變量進行賦值即賦值拷貝，這是一個性能上的開銷。從下面的測試輸出能看得出臨時變量的地址是不會變的，而且與切片的地址完全不同。如果切片元素包含字符串的話，用range遍歷和直接尋址遍歷的性能差別還是很顯著的。

package main

import (
	"fmt"
	"time"
)

type Person struct {
	Name     string
	Gender   string
	Experience string
}

func main(){
	persons := make([]Person,8)
	persons[0] = Person{"David","Male","This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!"}
	persons[1] = Person{"Jenny","Female","This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!"}
	persons[2] = Person{"Tom","Male","This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!"}
	persons[3] = Person{"Lucy","Female","This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!"}
	persons[4] = Person{"David","Male","This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!"}
	persons[5] = Person{"Jenny","Female","This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!"}
	persons[6] = Person{"Tom","Male","This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!"}
	persons[7] = Person{"Lucy","Female","This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!"}

	start := time.Now()
	for _,person := range persons{
		if person.Gender == "Male"{
			fmt.Printf("%p %v\n", &person, person)
		}
	}
	fmt.Printf("%v\n", time.Now().Sub(start))

	start = time.Now()
	for i:=0;i<len(persons);i++{
		if persons[i].Gender == "Male"{
			fmt.Printf("%p %v\n", &persons[i], persons[i])
		}
	}
	fmt.Printf("%v\n", time.Now().Sub(start))
}

輸出：

0xc00009a000 {David Male This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!}
0xc00009a000 {Tom Male This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!}
0xc00009a000 {David Male This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!}
0xc00009a000 {Tom Male This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!}
112.416µs
0xc000094180 {David Male This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!}
0xc0000941e0 {Tom Male This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!}
0xc000094240 {David Male This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!}
0xc0000942a0 {Tom Male This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!This is a long text!}
22.313µs