From 12dac713000661773c0070300f4370445362d8c2 Mon Sep 17 00:00:00 2001
From: Arthur Kushman <zeusakm@gmail.com>
Date: Thu, 4 May 2023 11:21:32 +0300
Subject: [PATCH] #67: Implement ConcatFast that concatenates strings faster
 than strings.Builder (#68)

---
 str.go      | 21 +++++++++++++
 str_test.go | 90 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 110 insertions(+), 1 deletion(-)

diff --git a/str.go b/str.go
index 4ef2535..d107ba9 100644
--- a/str.go
+++ b/str.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net/url"
 	"strings"
+	"unsafe"
 )
 
 type replaceParams struct {
@@ -129,3 +130,23 @@ func HTTPBuildQuery(pairs map[string]interface{}) string {
 
 	return q.Encode()
 }
+
+// ConcatFast concatenates strings faster than strings.Builder (see benchmarks)
+func ConcatFast(s ...string) string {
+	l := len(s)
+	if l == 0 {
+		return ""
+	}
+
+	n := 0
+	for i := 0; i < l; i++ {
+		n += len(s[i])
+	}
+
+	b := make([]byte, 0, n)
+	for i := 0; i < l; i++ {
+		b = append(b, s[i]...)
+	}
+
+	return *(*string)(unsafe.Pointer(&b))
+}
diff --git a/str_test.go b/str_test.go
index d07a64f..b121073 100644
--- a/str_test.go
+++ b/str_test.go
@@ -1,10 +1,15 @@
 package pgo_test
 
 import (
+	"math/rand"
+	"strings"
 	"testing"
+	"time"
 
-	"github.com/arthurkushman/pgo"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/arthurkushman/pgo"
 )
 
 func TestStrReplace(t *testing.T) {
@@ -74,3 +79,86 @@ func TestHTTPBuildQuery(t *testing.T) {
 	queryStr2 := pgo.HTTPBuildQuery(map[string]interface{}{})
 	assert.Empty(t, queryStr2, "built str from an empty map must be empty")
 }
+
+func TestConcatFast(t *testing.T) {
+	tests := []struct {
+		name   string
+		s      []string
+		result string
+	}{
+		{
+			name:   "concat 3 strings",
+			s:      []string{"foo", "bar", "bazzz"},
+			result: "foobarbazzz",
+		},
+		{
+			name:   "concat 0 strings",
+			s:      []string{},
+			result: "",
+		},
+		{
+			name: "concat random strings",
+			s: []string{"impEdfCJyek3jn5kj3nkj35nkj35nkj3nkj3n5kjn3kjn35kjn5", "IpDtUOSwMy", "sMIaQYdeON", "TZTwRNgZfx",
+				"kybtlfzfJa", "UJQJXhknLe", "GKDmxroeFv",
+				"ifguLESWvm333334241341231242414k12m4k1m24k1m2k4m1k24n1l2n41ln41lk2n4k12"},
+			result: "impEdfCJyek3jn5kj3nkj35nkj35nkj3nkj3n5kjn3kjn35kjn5IpDtUOSwMysMIaQYdeONTZTwRNgZfxkybtlfzfJaUJQJXhknLeGKDmxroeFvifguLESWvm333334241341231242414k12m4k1m24k1m2k4m1k24n1l2n41ln41lk2n4k12",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			resStr := pgo.ConcatFast(tc.s...)
+			require.Equal(t, tc.result, resStr)
+		})
+	}
+}
+
+func BenchmarkConcatFast(b *testing.B) {
+	s := generateRandomSliceOfStrings()
+	for i := 0; i < b.N; i++ {
+		pgo.ConcatFast(s...)
+	}
+}
+
+func BenchmarkConcatFast2(b *testing.B) {
+	s := generateRandomSliceOfStrings()
+	for i := 0; i < b.N; i++ {
+		stringBuilder(s...)
+	}
+}
+
+func generateRandomSliceOfStrings() []string {
+	const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+
+	rand.Seed(time.Now().UnixNano())
+	s := make([]string, 15)
+	for i := range s {
+		bt := make([]byte, 10)
+		for j := range bt {
+			bt[j] = letterBytes[rand.Intn(len(letterBytes))]
+		}
+		s[i] = string(bt)
+	}
+
+	return s
+}
+
+func stringBuilder(s ...string) string {
+	l := len(s)
+	if l == 0 {
+		return ""
+	}
+
+	b := strings.Builder{}
+	n := 0
+	for i := 0; i < l; i++ {
+		n += len(s[i])
+	}
+
+	b.Grow(n)
+	for i := 0; i < l; i++ {
+		b.WriteString(s[i])
+	}
+
+	return b.String()
+}