Benchmarking various ways of concatenating strings in Go

join_test.go

package join

import (
	"fmt"
	"strings"
	"testing"
)

var (
	testData = []string{"a", "b", "c", "d", "e"}
)

func BenchmarkJoin(b *testing.B) {
	for i := 0; i < b.N; i++ {
		s := strings.Join(testData, ":")
		_ = s
	}
}

func BenchmarkSprintf(b *testing.B) {
	for i := 0; i < b.N; i++ {
		s := fmt.Sprintf("%s:%s:%s:%s:%s", testData[0], testData[1], testData[2], testData[3], testData[4])
		_ = s
	}
}

func BenchmarkConcat(b *testing.B) {
	for i := 0; i < b.N; i++ {
		s := testData[0] + ":" + testData[1] + ":" + testData[2] + ":" + testData[3] + ":" + testData[4]
		_ = s
	}
}

just run with new go version

package benchmark

import (
	"bytes"
	"fmt"
	"strings"
	"testing"
)

var (
	testData = []string{"a", "b", "c", "d", "e"}
)

func BenchmarkJoin(b *testing.B) {
	for i := 0; i < b.N; i++ {
		s := strings.Join(testData, ":")
		_ = s
	}
}

func BenchmarkSprintf(b *testing.B) {
	for i := 0; i < b.N; i++ {
		s := fmt.Sprintf("%s:%s:%s:%s:%s", testData[0], testData[1], testData[2], testData[3], testData[4])
		_ = s
	}
}

func BenchmarkConcat(b *testing.B) {
	for i := 0; i < b.N; i++ {
		s := testData[0] + ":"
		s += testData[1] + ":"
		s += testData[2] + ":"
		s += testData[3] + ":"
		s += testData[4]
		_ = s
	}
}

func BenchmarkConcatOneLine(b *testing.B) {
	for i := 0; i < b.N; i++ {
		s := testData[0] + ":" +
			testData[1] + ":" +
			testData[2] + ":" +
			testData[3] + ":" +
			testData[4]
		_ = s
	}
}

func BenchmarkBuffer(b *testing.B) {
	for i := 0; i < b.N; i++ {
		var b bytes.Buffer
		b.WriteString(testData[0])
		b.WriteByte(':')
		b.WriteString(testData[1])
		b.WriteByte(':')
		b.WriteString(testData[2])
		b.WriteByte(':')
		b.WriteString(testData[3])
		b.WriteByte(':')
		b.WriteString(testData[4])
		s := b.String()
		_ = s
	}
}

func BenchmarkBufferWithReset(b *testing.B) {
	var buf bytes.Buffer

	for i := 0; i < b.N; i++ {
		buf.Reset()

		buf.WriteString(testData[0])
		buf.WriteByte(':')
		buf.WriteString(testData[1])
		buf.WriteByte(':')
		buf.WriteString(testData[2])
		buf.WriteByte(':')
		buf.WriteString(testData[3])
		buf.WriteByte(':')
		buf.WriteString(testData[4])
		s := buf.String()
		_ = s
	}
}

func BenchmarkBufferFprintf(b *testing.B) {
	buf := &bytes.Buffer{}

	for i := 0; i < b.N; i++ {
		buf.Reset()

		fmt.Fprintf(buf, "%s:%s:%s:%s:%s", testData[0], testData[1], testData[2], testData[3], testData[4])
		s := buf.String()
		_ = s
	}

}

func BenchmarkBufferStringBuilder(b *testing.B) {
	var buf strings.Builder

	for i := 0; i < b.N; i++ {
		buf.Reset()

		buf.WriteString(testData[0])
		buf.WriteByte(':')
		buf.WriteString(testData[1])
		buf.WriteByte(':')
		buf.WriteString(testData[2])
		buf.WriteByte(':')
		buf.WriteString(testData[3])
		buf.WriteByte(':')
		buf.WriteString(testData[4])
		s := buf.String()
		_ = s
	}
}

Environment:

• Intel(R) Core(TM) i7-6700HQ CPU @ 2.60GHz

• Go 1.14.2

go test -v -run=BENCH -bench=. -benchtime 5s -benchmem

goos: linux
goarch: amd64
BenchmarkJoin-8                  	74904537	        80.1 ns/op	      16 B/op	       1 allocs/op
BenchmarkSprintf-8               	15639747	       377 ns/op	      96 B/op	       6 allocs/op
BenchmarkConcat-8                	31753981	       188 ns/op	      32 B/op	       4 allocs/op
BenchmarkConcatOneLine-8         	88710248	        73.6 ns/op	       0 B/op	       0 allocs/op
BenchmarkBuffer-8                	61480548	        97.7 ns/op	      64 B/op	       1 allocs/op
BenchmarkBufferWithReset-8       	100000000	        60.2 ns/op	       0 B/op	       0 allocs/op
BenchmarkBufferFprintf-8         	16348393	       365 ns/op	      80 B/op	       5 allocs/op
BenchmarkBufferStringBuilder-8   	69169862	        85.1 ns/op	      24 B/op	       2 allocs/op

Hm. Seems that concat done in one line might be the winner here: it's the easiest to read, does not allocate anything, and is only beaten by writing to a buffer, which, although being cool as a concept, looks much weirder (especially for someone who comes from other programming languages where string concatenation is simply done with an operator between strings...). I'm sure that there are many special cases where it's worth the extra typing effort to use buffers, but... I'm a big fan of keeping things simple and understandable. If the 'cost' of doing so is just a dozen extra nanoseconds... it's worth the trouble, IMHO.

Use the code from @RezaOptic above

go version go1.17 darwin/amd64

Results

goos: darwin
goarch: amd64
pkg: ***
cpu: Intel(R) Core(TM) i7-4980HQ CPU @ 2.80GHz
BenchmarkJoin-8                  	18044035	        74.59 ns/op	      16 B/op	       1 allocs/op
BenchmarkSprintf-8               	 3249290	       393.9 ns/op	      96 B/op	       6 allocs/op
BenchmarkConcat-8                	 6670018	       257.7 ns/op	      32 B/op	       4 allocs/op
BenchmarkConcatOneLine-8         	20360762	        94.10 ns/op	       0 B/op	       0 allocs/op
BenchmarkBuffer-8                	16493529	       102.2 ns/op	      64 B/op	       1 allocs/op
BenchmarkBufferWithReset-8       	29284802	        51.32 ns/op	       0 B/op	       0 allocs/op
BenchmarkBufferFprintf-8         	 2917341	       392.3 ns/op	      80 B/op	       5 allocs/op
BenchmarkBufferStringBuilder-8   	15469124	        93.51 ns/op	      24 B/op	       2 allocs/op