sort_test.go

package main

import (
	"encoding/base64"
	"math/rand"
	"testing"

	"x/esort"

	"golang.org/x/exp/constraints"
	"golang.org/x/exp/slices"
)

type Person struct {
	GivenName string
	ID        int
}

type LessFn[T any] func(l, r T) bool

func (f LessFn[T]) Reverse(l, r T) bool {
	return f(r, l)
}

type Chain[T any] []LessFn[T]

func (c Chain[T]) Less(l, r T) bool {
	for _, f := range c {
		switch {
		case f(l, r):
			return true
		case f(r, l):
			return false
		}
	}
	return false
}

func Less[T constraints.Ordered](l, r T) bool {
	return l < r
}

func By[C any, F constraints.Ordered](by func(C) F) LessFn[C] {
	return func(l, r C) bool { return Less(by(l), by(r)) }
}

func ByFunc[C, F any](by func(C) F, less func(F, F) bool) LessFn[C] {
	return func(l, r C) bool { return less(by(l), by(r)) }
}

func genPeople(r *rand.Rand, n int) []Person {
	p := make([]Person, n)
	for i := range p {
		buf := make([]byte, r.Intn(5))
		r.Read(buf)
		p[i].GivenName = base64.RawURLEncoding.EncodeToString(buf)
		p[i].ID = r.Intn(n)
	}
	return p
}

const N = 1000000

func benchSorter(b *testing.B, sort func([]Person)) {
	r := rand.New(rand.NewSource(0))
	p := genPeople(r, N)

	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		b.StopTimer()
		r.Shuffle(N, func(i, j int) { p[i], p[j] = p[j], p[i] })
		b.StartTimer()
		sort(p)
	}
}

func BenchmarkMy(b *testing.B) {
	benchSorter(b, func(p []Person) {
		cmp := Chain[Person]{
			By(func(p Person) string { return p.GivenName }).Reverse,
			By(func(p Person) int { return p.ID }),
		}
		slices.SortFunc(p, cmp.Less)
	})
}

func BenchmarkMatt(b *testing.B) {
	benchSorter(b, func(p []Person) {
		sorter := new(esort.Sorter[Person]).
			ByString(func(p Person) string { return p.GivenName }, esort.Desc).
			ByInt(func(p Person) int { return p.ID }, esort.Asc)
		slices.SortFunc(p, sorter.Less)
	})
}