```
import "fmt"
func main() {
var a []int
printSlice("a", a)
// append works on nil slices.
a = append(a, 0)
printSlice("a", a)
// the slice grows as needed.
a = append(a, 1)
printSlice("a", a)
// we can add more than one element at a time.
a = append(a, 2, 3, 4)
printSlice("a", a)
}
func printSlice(s string, x []int) {
fmt.Printf("%s len=%d cap=%d %v\n",
s, len(x), cap(x), x)
}
```
运行结果：
a len=0 cap=0 []
a len=1 cap=2 [0]
a len=2 cap=2 [0 1]
a len=5 cap=8 [0 1 2 3 4]
求大神指导下里面的cap值都是怎么得来的，特别是第二个是2，第三个也是2
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