Slow generic sorting

slowsort.go

package slowsort

import (
	"reflect"
	"sort"
)

func Sort(sl interface{}, less interface{}) {
	rsl := reflect.ValueOf(sl)
	if rsl.Kind() != reflect.Slice {
		panic("first parameter must be a slice")
	}
	slt := rsl.Type()
	lessfn := reflect.ValueOf(less)
	if lessfn.Kind() != reflect.Func {
		panic("second parameter must be a function")
	}
	fnt := lessfn.Type()
	if fnt.NumIn() != 2 || fnt.NumOut() != 1 {
		panic("must be a func(a,b) bool")
	}
	if fnt.Out(0) != reflect.TypeOf(true) {
		panic("return value of less function must be a bool")
	}
	sorter := &slowSorter{
		len:    rsl.Len(),
		sl:     rsl,
		lessfn: lessfn,
		tmp:    reflect.New(slt.Elem()).Elem(),
	}
	sort.Sort(sorter)
}

type slowSorter struct {
	len    int
	lessfn reflect.Value
	sl     reflect.Value
	tmp    reflect.Value
}

func (ss *slowSorter) Len() int {
	return ss.len
}

func (ss *slowSorter) Less(i, j int) bool {
	iv, jv := ss.sl.Index(i), ss.sl.Index(j)
	ret := ss.lessfn.Call([]reflect.Value{iv, jv})
	return ret[0].Bool()
}

func (ss *slowSorter) Swap(i, j int) {
	iv, jv := ss.sl.Index(i), ss.sl.Index(j)
	ss.tmp.Set(jv)
	jv.Set(iv)
	iv.Set(ss.tmp)
}

slowsort_test.go

package slowsort

import (
	"testing"
	"reflect"
	"sort"
)

func TestInts(t *testing.T) {
	x := []int{5, 3, 1, 9}
	Sort(x, func(a, b int) bool {
		return a < b
	})
	expected := []int{1, 3, 5, 9}
	if !reflect.DeepEqual(expected, x) {
		t.Errorf("Expected %v, got %v", expected, x)
	}
}

func TestStrings(t *testing.T) {
	x := []string{"foo", "bar", "Baz", "botz", "whuz"}
	Sort(x, func(a, b string) bool {
		return a < b
	})
	expected := append([]string(nil), x...)
	sort.Strings(expected)
	if !reflect.DeepEqual(expected, x) {
		t.Errorf("Expected %v, got %v", expected, x)
	}
}

type mystruct struct {
	x int
	y int
}

func TestStructs(t *testing.T) {
	x := []mystruct{{5, 0}, {3, 0}, {1, 0}, {9, 0}}
	Sort(x, func(a, b mystruct) bool {
		return a.x < b.x
	})
	expected := []mystruct{{1, 0}, {3, 0}, {5, 0}, {9, 0}}
	if !reflect.DeepEqual(expected, x) {
		t.Errorf("Expected %v, got %v", expected, x)
	}
}

func TestStructPtrs(t *testing.T) {
	x := []*mystruct{&mystruct{5, 0}, &mystruct{3, 0}, &mystruct{1, 0}, &mystruct{9, 0}}
	Sort(x, func(a, b *mystruct) bool {
		return a.x < b.x
	})
	expected := []*mystruct{&mystruct{1, 0}, &mystruct{3, 0}, &mystruct{5, 0}, &mystruct{9, 0}}
	if !reflect.DeepEqual(expected, x) {
		t.Errorf("Expected %v, got %v", expected, x)
	}
}

func TestFromMap(t *testing.T) {
	m := map[string]int{
		"A": 3,
		"B": 2,
		"C": 1,
		"D": 4,
	}
	var keys []string
	for k := range m {
		keys = append(keys, k)
	}
	Sort(keys, func(a, b string) bool {
		return m[a] < m[b]
	})
	expected := []string{"C", "B", "A", "D"}
	if !reflect.DeepEqual(expected, keys) {
		t.Errorf("TestFromMap: expected %v, got %v", expected, keys)
	}
}

var unsorted = []int{-9, 9, 3, 1, 4, 2, 11, 66, 7, 0}

func BenchmarkSlowSort(b *testing.B) {
	data := make([]int, len(unsorted))
	for i := 0; i < b.N; i++ {
		copy(data, unsorted)
		Sort(data, func(a, b int) bool {
			return a < b
		})
	}
}

func BenchmarkSlowSortBig(b *testing.B) {
	data := make([]int, 2048)
	for i := 0; i < b.N; i++ {
		for i := range data {
			data[i] = i
		}
		Sort(data, func(a, b int) bool {
			return a < b
		})
	}
}

func BenchmarkSort(b *testing.B) {
	data := make([]int, len(unsorted))
	for i := 0; i < b.N; i++ {
		copy(data, unsorted)
		sort.Ints(data)
	}
}