解释（阅读内联 cmets）：
package main
import (
"fmt"
)
var a = make([]int, 7, 8)
// A slice is a descriptor of an array segment.
// It consists of a pointer to the array, the length of the segment, and its capacity (the maximum length of the segment).
// The length is the number of elements referred to by the slice.
// The capacity is the number of elements in the underlying array (beginning at the element referred to by the slice pointer).
// |-> Refer to: https://blog.golang.org/go-slices-usage-and-internals -> "Slice internals" section
func Test(slice []int) {
// slice receives a copy of slice `a` which point to the same array as slice `a`
slice[6] = 10
slice = append(slice, 100)
// since `slice` capacity is 8 & length is 7, it can add 100 and make the length 8
fmt.Println(slice, len(slice), cap(slice), " << Test 1")
slice = append(slice, 200)
// since `slice` capacity is 8 & length also 8, slice has to make a new slice
// - with double of size with point to new array (see Reference 1 below).
// (I'm also confused, why not (n+1)*2=20). But make a new slice of 16 capacity).
slice[6] = 13 // make sure, it's a new slice :)
fmt.Println(slice, len(slice), cap(slice), " << Test 2")
}
func main() {
for i := 0; i < 7; i++ {
a[i] = i
}
fmt.Println(a, len(a), cap(a))
Test(a)
fmt.Println(a, len(a), cap(a))
fmt.Println(a[:cap(a)], len(a), cap(a))
// fmt.Println(a[:cap(a)+1], len(a), cap(a)) -> this'll not work
}
输出：
[0 1 2 3 4 5 6] 7 8
[0 1 2 3 4 5 10 100] 8 8 << Test 1
[0 1 2 3 4 5 13 100 200] 9 16 << Test 2
[0 1 2 3 4 5 10] 7 8
[0 1 2 3 4 5 10 100] 7 8
参考1：https://blog.golang.org/go-slices-usage-and-internals
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
}