sort.Sort不修改数组

The following code should create an array of ints (a) and sort it, but sort.Sort does not appear to modify the variable.

package main

import (
    "fmt"
    "sort"
)

type IntArray [5]int

type byNum [5]int
func (s byNum) Len() int {
    return len(s)
}
func (s byNum) Swap(i, j int) {
    s[i], s[j] = s[j], s[i]
}
func (s byNum) Less(i, j int) bool {
    return s[i] < s[j]
}

func main() {
    a := IntArray{5,3,4,1,2}

    fmt.Println(a)
    sort.Sort(byNum(a))
    fmt.Println(a)
}

https://play.golang.org/p/bhcwgosqvis

[5 3 4 1 2]
[5 3 4 1 2]

Program exited.

Why does this not work?

The problem is that the Swap method is changing the argument array, not the array in the caller.

Fix by declaring byNum as a slice:

type byNum []int

...

sort.Sort(byNum(a[:]))

In this call, the backing array of the slice argument is the array that you want to modify.

Run it on the playground.