发布于 2016-10-24 11:23:26 | 179 次阅读 | 评论: 0 | 来源: 网友投递
Go语言
Go是一种新的语言,一种并发的、带垃圾回收的、快速编译的语言。Go是谷歌2009年发布的第二款编程语言。2009年7月份,谷歌曾发布了Simple语言,它是用来开发Android应用的一种BASIC语言。
一、类型
数组是值类型,将一个数组赋值给另一个数组时,传递的是一份拷贝。
切片是引用类型,切片包装的数组称为该切片的底层数组。
我们来看一段代码
//a是一个数组,注意数组是一个固定长度的,初始化时候必须要指定长度,不指定长度的话就是切片了
a := [3]int{1, 2, 3}
//b是数组,是a的一份拷贝
b := a
//c是切片,是引用类型,底层数组是a
c := a[:]
for i := 0; i < len(a); i++ {
a[i] = a[i] + 1
}
//改变a的值后,b是a的拷贝,b不变,c是引用,c的值改变
fmt.Println(a) //[2,3,4]
fmt.Println(b) //[1 2 3]
fmt.Println(c) //[2,3,4]
二、make
make 只能用于slice
, map
和 channel
, 所以下面一段代码生成了一个slice
,是引用类型
s1 := make([]int, 0, 3)
for i := 0; i < cap(s1); i++ {
s1 = append(s1, i)
}
s2 := s1
for i := 0; i < len(a); i++ {
s1[i] = s1[i] + 1
}
fmt.Println(s1) //[1 2 3]
fmt.Println(s2) //[1 2 3]
三、当对slice append 超出底层数组的界限时
//n1是n2的底层数组
n1 := [3]int{1, 2, 3}
n2 := n1[0:3]
fmt.Println("address of items in n1: ")
for i := 0; i < len(n1); i++ {
fmt.Printf("%p\n", &n1[i])
}
//address of items in n1:
//0xc20801e160
//0xc20801e168
//0xc20801e170
fmt.Println("address of items in n2: ")
for i := 0; i < len(n2); i++ {
fmt.Printf("%p\n", &n2[i])
}
//address of items in n2:
//0xc20801e160
//0xc20801e168
//0xc20801e170
//对n2执行append操作后,n2超出了底层数组n1的j
n2 = append(n2, 1)
fmt.Println("address of items in n1: ")
for i := 0; i < len(n1); i++ {
fmt.Printf("%p\n", &n1[i])
}
//address of items in n1:
//0xc20801e160
//0xc20801e168
//0xc20801e170
fmt.Println("address of items in n2: ")
for i := 0; i < len(n2); i++ {
fmt.Printf("%p\n", &n2[i])
}
//address of items in n2:
//0xc20803a2d0
//0xc20803a2d8
//0xc20803a2e0
//0xc20803a2e8
四、引用“失效”
实现了删除slice
最后一个item
的函数
func rmLast(a []int) {
fmt.Printf("[rmlast] the address of a is %p", a)
a = a[:len(a)-1]
fmt.Printf("[rmlast] after remove, the address of a is %p", a)
}
调用此函数后,发现原来的slice
并没有改变
func main() {
xyz := []int{1, 2, 3, 4, 5, 6, 7, 8, 9}
fmt.Printf("[main] the address of xyz is %p\n", xyz)
rmLast(xyz)
fmt.Printf("[main] after remove, the address of xyz is %p\n", xyz)
fmt.Printf("%v", xyz) //[1 2 3 4 5 6 7 8 9]
}
打印出来的结果如下:
[main] the address of xyz is 0xc2080365f0
[rmlast] the address of a is 0xc2080365f0
[rmlast] after remove, the address of a is 0xc2080365f0
[main] after remove, the address of xyz is 0xc2080365f0
[1 2 3 4 5 6 7 8 9]
这里直接打印了slice
的指针值,因为slice
是引用类型,所以指针值都是相同的,我们换成打印slice
的地址看下
func rmLast(a []int) {
fmt.Printf("[rmlast] the address of a is %p", &a)
a = a[:len(a)-1]
fmt.Printf("[rmlast] after remove, the address of a is %p", &a)
}
func main() {
xyz := []int{1, 2, 3, 4, 5, 6, 7, 8, 9}
fmt.Printf("[main] the address of xyz is %p\n", &xyz)
rmLast(xyz)
fmt.Printf("[main] after remove, the address of xyz is %p\n", &xyz)
fmt.Printf("%v", xyz) //[1 2 3 4 5 6 7 8 9]
}
结果:
[main] the address of xyz is 0xc20801e1e0
[rmlast] the address of a is 0xc20801e200
[rmlast] after remove, the address of a is 0xc20801e200
[main] after remove, the address of xyz is 0xc20801e1e0
[1 2 3 4 5 6 7 8 9]
这次可以看到slice
作为函数参数传入函数时,实际上也是拷贝了一份slice
,因为slice
本身是个指针,所以从现象来看,slice
是引用类型
总结
以上就是这篇文章的全部内容,希望对大家的学习或者工作带来一定的帮助,如果有疑问大家可以留言交流。