How to Efficiently Concatenate Strings in Go

7种拼接方式

String Concat

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str += "hello-world"

String Sprintf

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str = fmt.Sprintf("%s%s", str, "hello-world")

String Join

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str = strings.Join([]string{str, "hello-world"}, "")

Buffer Write

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buf := new(bytes.Buffer)
buf.WriteString("hello-world")
str := buf.String()

Bytes Append

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var b []byte
s := "hello-world"
b = append(b, s...)
str := string(b)

String Copy

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ts := "hello-world"
n := 5
tsl := len(ts) * n
bs := make([]byte, tsl)
bl := 0

for bl < tsl {
    bl += copy(bs[bl:], ts)
}

str := string(bs)

String Builder

From Go 1.10 there is a strings.Builder type

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var builder strings.Builder
builder.WriteString("hello-world")
str := builder.String()

benchmark

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package main

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

const (
    sss = "xfoasneobfasieongasbg"
    cnt = 10000
)

var (
    bbb      = []byte(sss)
    expected = strings.Repeat(sss, cnt)
)

func BenchmarkCopyPreAllocate(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        bs := make([]byte, cnt*len(sss))
        bl := 0
        for i := 0; i < cnt; i++ {
            bl += copy(bs[bl:], sss)
        }
        result = string(bs)
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}

func BenchmarkAppendPreAllocate(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        data := make([]byte, 0, cnt*len(sss))
        for i := 0; i < cnt; i++ {
            data = append(data, sss...)
        }
        result = string(data)
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}

func BenchmarkBufferPreAllocate(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        buf := bytes.NewBuffer(make([]byte, 0, cnt*len(sss)))
        for i := 0; i < cnt; i++ {
            buf.WriteString(sss)
        }
        result = buf.String()
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}

func BenchmarkCopy(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        data := make([]byte, 0, 64) // same size as bootstrap array of bytes.Buffer
        for i := 0; i < cnt; i++ {
            off := len(data)
            if off+len(sss) > cap(data) {
                temp := make([]byte, 2*cap(data)+len(sss))
                copy(temp, data)
                data = temp
            }
            data = data[0 : off+len(sss)]
            copy(data[off:], sss)
        }
        result = string(data)
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}

func BenchmarkCopyX(b *testing.B) {
    bs := make([]byte, b.N)
    bl := 0

    b.ResetTimer()
    for n := 0; n < b.N; n++ {
        bl += copy(bs[bl:], "x")
    }
    b.StopTimer()

    if s := strings.Repeat("x", b.N); string(bs) != s {
        b.Errorf("unexpected result; got=%s, want=%s", string(bs), s)
    }
}

func BenchmarkAppend(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        data := make([]byte, 0, 64)
        for i := 0; i < cnt; i++ {
            data = append(data, sss...)
        }
        result = string(data)
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}

func BenchmarkBufferWrite(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        var buf bytes.Buffer
        for i := 0; i < cnt; i++ {
            buf.Write(bbb)
        }
        result = buf.String()
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}

func BenchmarkBufferWriteString(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        var buf bytes.Buffer
        for i := 0; i < cnt; i++ {
            buf.WriteString(sss)
        }
        result = buf.String()
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}

func BenchmarkConcatString(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        var str string
        for i := 0; i < cnt; i++ {
            str += sss
        }
        result = str
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}

func BenchmarkConcat(b *testing.B) {
    var str string
    for n := 0; n < b.N; n++ {
        str += "x"
    }
    b.StopTimer()

    if s := strings.Repeat("x", b.N); str != s {
        b.Errorf("unexpected result; got=%s, want=%s", str, s)
    }
}

func BenchmarkBuffer(b *testing.B) {
    var buffer bytes.Buffer
    for n := 0; n < b.N; n++ {
        buffer.WriteString("x")
    }
    b.StopTimer()

    if s := strings.Repeat("x", b.N); buffer.String() != s {
        b.Errorf("unexpected result; got=%s, want=%s", buffer.String(), s)
    }
}

// Go 1.10
func BenchmarkStringBuilderX(b *testing.B) {
    var strBuilder strings.Builder

    b.ResetTimer()
    for n := 0; n < b.N; n++ {
        strBuilder.WriteString("x")
    }
    b.StopTimer()

    if s := strings.Repeat("x", b.N); strBuilder.String() != s {
        b.Errorf("unexpected result; got=%s, want=%s", strBuilder.String(), s)
    }
}

func BenchmarkStringBuilder(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        var builder strings.Builder

        for i := 0; i < cnt; i++ {
            builder.WriteString(sss)
        }

        result = builder.String()
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}

func BenchmarkStringConcat(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        var str string
        for i := 0; i < cnt; i++ {
            str += sss
        }
        result = str
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}

func BenchmarkStringSprintf(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        var str string
        for i := 0; i < cnt; i++ {
            str = fmt.Sprintf("%s%s", str, sss)
        }
        result = str
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}

func BenchmarkStringJoin(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        var str string
        for i := 0; i < cnt; i++ {
            str = strings.Join([]string{str, sss}, "")
        }
        result = str
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}

func BenchmarkBytesAppend(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        var bbb []byte

        for i := 0; i < cnt; i++ {
            bbb = append(bbb, sss...)
        }
        result = string(bbb)
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}

func BenchmarkStringCopy(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        tsl := len(sss) * cnt
        bs := make([]byte, tsl)
        bl := 0

        for bl < tsl {
            bl += copy(bs[bl:], sss)
        }

        result = string(bs)
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}

Test Results:

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go test -v strings_concat_benchmark_test.go -bench=. -benchmem
goos: darwin
goarch: amd64
BenchmarkCopyPreAllocate-4          8043            125464 ns/op          425984 B/op          2 allocs/op
BenchmarkAppendPreAllocate-4        9818            126881 ns/op          425985 B/op          2 allocs/op
BenchmarkBufferPreAllocate-4        7656            161158 ns/op          425984 B/op          2 allocs/op
BenchmarkCopy-4                     4903            250800 ns/op          929185 B/op         13 allocs/op
BenchmarkCopyX-4                263460769                5.19 ns/op            0 B/op          0 allocs/op
BenchmarkAppend-4                   3820            384086 ns/op         1333122 B/op         24 allocs/op
BenchmarkBufferWrite-4              3626            299617 ns/op          929250 B/op         14 allocs/op
BenchmarkBufferWriteString-4        4428            286061 ns/op          929249 B/op         14 allocs/op
BenchmarkConcatString-4                5         210904237 ns/op        1086401044 B/op    10037 allocs/op
BenchmarkConcat-4                1000000            118204 ns/op          503996 B/op          1 allocs/op
BenchmarkBuffer-4               132420037                8.74 ns/op            2 B/op          0 allocs/op
BenchmarkStringBuilderX-4       418325671                5.97 ns/op            6 B/op          0 allocs/op
BenchmarkStringBuilder-4            3890            310115 ns/op         1120224 B/op         25 allocs/op
BenchmarkStringConcat-4                5         229555747 ns/op        1086401641 B/op    10050 allocs/op
BenchmarkStringSprintf-4               3         451219496 ns/op        2068371440 B/op    35040 allocs/op
BenchmarkStringJoin-4                  4         281371101 ns/op        1086401946 B/op    10058 allocs/op
BenchmarkBytesAppend-4              3406            406706 ns/op         1333218 B/op         26 allocs/op
BenchmarkStringCopy-4               9100            133990 ns/op          425984 B/op          2 allocs/op
PASS
ok      command-line-arguments  148.510s

参考