func copy(dst, src []Type) int
The copy built-in function copies elements from a source slice into a destination slice. (As a special case, it also will copy bytes from a string to a slice of bytes.) The source and destination may overlap. Copy returns the number of elements copied, which will be the minimum of len(src) and len(dst).

package main


import (
    “fmt”
)

func main() {
    d := []int{1, 2, 3}
    s := d[1:]
    fmt.Println(“Before copying: “, “source is: “, s, “destination is: “, d)
    fmt.Println(copy(d, s))
    fmt.Println(“After copying: “, “source is: “, s, “destination is: “, d)
    s = []int{1, 2, 3}
    d = s[1:]
    fmt.Println(“Before copying: “, “source is: “, s, “destination is: “, d)
    fmt.Println(copy(d, s))
    fmt.Println(“After copying: “, “source is: “, s, “destination is: “, d)
}

结果：

Before copying:  source is:  [2 3] destination is:  [1 2 3]
2
After copying:  source is:  [3 3] destination is:  [2 3 3]
Before copying:  source is:  [1 2 3] destination is:  [2 3]
2
After copying:  source is:  [1 1 2] destination is:  [1 2]