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
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//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
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