Golong字符串拼接性能优化及原理介绍

func plusConcat(n int, s string) string {
	var d string
	for i := 0; i < n; i++ {
		d += s
	}
	return d
}

func sprintfConcat(n int, s string) string {
	var d string
	for i := 0; i < n; i++ {
		d = fmt.Sprintf("%s%s", d, s)
	}
	return d
}

func builderConcat(n int, s string) string {
	var sb = new(strings.Builder)
	for i := 0; i < n; i++ {
		sb.WriteString(s)
	}
	return sb.String()
}

func bufferConcat(n int, s string) string {
	var bb = new(bytes.Buffer)
	for i := 0; i < n; i++ {
		bb.WriteString(s)
	}
	return bb.String()
}

func byteConcat(n int, s string) string {
	var b = make([]byte, 0)
	for i := 0; i < n; i++ {
		b = append(b, s...)
	}
	return string(b)
}

func preByteConcat(n int, s string) string {
	var b = make([]byte, 0, n*len(s))
	for i := 0; i < n; i++ {
		b = append(b, s...)
	}
	return string(b)
}

const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
func randomString(n int) string {
	b := make([]byte, n)
	for i := range b {
		b[i] = letterBytes[rand.Intn(len(letterBytes))]
	}
	return string(b)
}

func benchmark(b *testing.B, f func(int, string) string) {
	var str = randomString(10)
	for i := 0; i < b.N; i++ {
		f(10000, str)
	}
}
func BenchmarkPlusConcat(b *testing.B)    { benchmark(b, plusConcat) }
func BenchmarkSprintfConcat(b *testing.B) { benchmark(b, sprintfConcat) }
func BenchmarkBuilderConcat(b *testing.B) { benchmark(b, builderConcat) }
func BenchmarkBufferConcat(b *testing.B)  { benchmark(b, bufferConcat) }
func BenchmarkByteConcat(b *testing.B)    { benchmark(b, byteConcat) }
func BenchmarkPreByteConcat(b *testing.B) { benchmark(b, preByteConcat) }

func builderConcat(n int, s string) string {
	var sb = new(strings.Builder)
	sb.Grow(n * len(s))
	for i := 0; i < n; i++ {
		sb.WriteString(s)
	}
	return sb.String()
}

func (b *Buffer) String() string {
	if b == nil {
		// Special case, useful in debugging.
		return "<nil>"
	}
	return string(b.buf[b.off:])
}

// String returns the accumulated string.
func (b *Builder) String() string {
	return unsafe.String(unsafe.SliceData(b.buf), len(b.buf))
}