深入理解go slice结构

t := make([]byte, len(s), (cap(s)+1)*2)
copy(t, s)
s = t

func AppendByte(slice []byte, data ...byte) []byte {
    m := len(slice)
    n := m + len(data)
    if n > cap(slice) { // if necessary, reallocate
        // allocate double what's needed, for future growth.
        newSlice := make([]byte, (n+1)*2)
        copy(newSlice, slice)
        slice = newSlice
    }
    slice = slice[0:n]
    copy(slice[m:n], data)
    return slice
}

a := [4]int{0,1,2,3}
s := a[1:2] // {1}
return s

var digitRegexp = regexp.MustCompile("[0-9]+")

func FindDigits(filename string) []byte {
    b, _ := ioutil.ReadFile(filename)
    return digitRegexp.Find(b)
}

func CopyDigits(filename string) []byte {
    b, _ := ioutil.ReadFile(filename)
    b = digitRegexp.Find(b)
    c := make([]byte, len(b))
    copy(c, b)
    return c
}

package reflect

// SliceHeader和StringHeader具有相同的Data和Len，这导致[]byte可以直接转换成string，而不需要任何复制
type SliceHeader struct {
	Data uintptr
	Len  int
	Cap  int
}
type StringHeader struct {
	Data uintptr
	Len  int
}

func SliceByteAsString(b []byte) string {
    return *(*string)(unsafe.Pointer(&b))
}
func StringAsSliceByte(s string) []byte {
    p := unsafe.Pointer(&d)
    var b []byte
    hdr :=  (*reflect.SliceHeader)(unsafe.Pointer(&b))
    hdr.Data = uintptr(p)
    hdr.Cap = len(s)
    hdr.Len = len(s)
    return b
}

func Int64AsByteSlice(d int64) []byte {
    p := unsafe.Pointer(&d)
    var b []byte
    hdr :=  (*reflect.SliceHeader)(unsafe.Pointer(&b))
    hdr.Data = uintptr(p)
    hdr.Cap = 8
    hdr.Len = 8
    return b
}