golang builder,buffer,+的对比

• 使用buffer或是builder来拼接字符串，会比使用+或+=快

func BenchmarkBuffer(b *testing.B) {
	text := "test"
	b.ResetTimer()
	buffer := bytes.Buffer{}
	for i := 0; i < b.N; i++ {
		buffer.WriteString(text)
	}
	buffer.String()
}

func BenchmarkBuilder(b *testing.B) {
	text := "test"
	b.ResetTimer()
	builder := strings.Builder{}
	for i := 0; i < b.N; i++ {
		builder.WriteString(text)
	}
	builder.String()
}

func BenchmarkString(b *testing.B) {
	text := "test"
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		text += "test"
	}
}

结果

goos: windows
goarch: amd64
pkg: test/one
BenchmarkBuffer
BenchmarkBuffer-12         181560793             8.03 ns/op
BenchmarkBuilder
BenchmarkBuilder-12        360210758             3.86 ns/op
BenchmarkString
BenchmarkString-12           353895         96676 ns/op

func BenchmarkBuffer(b *testing.B) {
	text := ""
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		buffer := bytes.Buffer{}
		buffer.WriteString(text)
		buffer.WriteString(text)
		buffer.String()
	}
}

func BenchmarkBuilder(b *testing.B) {
	text := ""
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		builder := strings.Builder{}
		builder.WriteString(text)
		builder.WriteString(text)
		builder.String()
	}
}

func BenchmarkString(b *testing.B) {
	text := ""
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		text = ""
		text += ""
	}
}

结果

goos: windows
goarch: amd64
pkg: test/one
BenchmarkBuffer
BenchmarkBuffer-12         136879110             8.73 ns/op
BenchmarkBuilder
BenchmarkBuilder-12        499198370             2.44 ns/op
BenchmarkString
BenchmarkString-12         276599348             4.29 ns/op

第二种空字符串的可能在应用上基本不会用到，通常情况下我们用builder和buffer会比+快很多。

func (b *Builder) WriteString(s string) (int, error) {
	b.copyCheck()
	b.buf = append(b.buf, s...)
	return len(s), nil
}

builder的字符串相加就是直接用的append

func (b *Buffer) WriteString(s string) (n int, err error) {
	b.lastRead = opInvalid
	m, ok := b.tryGrowByReslice(len(s))
	if !ok {
		m = b.grow(len(s))
	}
	return copy(b.buf[m:], s), nil
}

buffer的字符串相加用的是copy，不同的是它会先去判断现有buf够不够长，不够的话会进行2倍的扩容

func concatstrings(buf *tmpBuf, a []string) string {
	idx := 0
	l := 0
	count := 0
	for i, x := range a {
		n := len(x)
		if n == 0 {
			continue
		}
		if l+n < l {
			throw("string concatenation too long")
		}
		l += n
		count++
		idx = i
	}
	if count == 0 {
		return ""
	}

	// If there is just one string and either it is not on the stack
	// or our result does not escape the calling frame (buf != nil),
	// then we can return that string directly.
	if count == 1 && (buf != nil || !stringDataOnStack(a[idx])) {
		return a[idx]
	}
	s, b := rawstringtmp(buf, l)
	for _, x := range a {
		copy(b, x)
		b = b[len(x):]
	}
	return s
}

而+号则是先把相加的字符串变成数组再设置总长度，最后才是拷贝