Go 连接字符串

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package hello

import "testing"

/*
=== RUN   TestStringConcat
    /Users/xxx/Codes/go/src/github.com/xxx/hello/hello_test.go:20: Hello World!
--- PASS: TestStringConcat (0.00s)
PASS
ok  	example.com/hello	0.014s
*/
func TestStringConcat(t *testing.T) {
  s := "Hello "
  s += "World!"
  t.Log(s)
}

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package hello

import (
  "fmt"
  "testing"
)

/*
=== RUN   TestStringSprintf
    /Users/xxx/Codes/go/src/github.com/xxx/hello/hello_test.go:18: Hello World!
--- PASS: TestStringSprintf (0.00s)
PASS
ok  	example.com/hello	0.010s
*/
func TestStringSprintf(t *testing.T) {
  s := "Hello "
  s = fmt.Sprintf("%s%s", s, "World!")
  t.Log(s)
}

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package hello

import (
  "strings"
  "testing"
)

/*
=== RUN   TestStringJoin
    /Users/xxx/Codes/go/src/github.com/xxx/hello/hello_test.go:18: Hello World!
--- PASS: TestStringJoin (0.00s)
PASS
ok  	example.com/hello	0.008s
*/
func TestStringJoin(t *testing.T) {
  s := "Hello "
  s = strings.Join([]string{s, "World!"}, "")
  t.Log(s)
}

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package hello

import (
  "bytes"
  "testing"
)

/*
=== RUN   TestBufferWrite
    /Users/xxx/Codes/go/src/github.com/xxx/hello/hello_test.go:20: Hello World!
--- PASS: TestBufferWrite (0.00s)
PASS
ok  	example.com/hello	0.010s
*/
func TestBufferWrite(t *testing.T) {
  buf := new(bytes.Buffer)
  buf.WriteString("Hello ")
  buf.WriteString("World!")
  s := buf.String()
  t.Log(s)
}

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package hello

import "testing"

/*
=== RUN   TestBytesAppend
    /Users/xxx/Codes/go/src/github.com/xxx/hello/hello_test.go:18: Hello
--- PASS: TestBytesAppend (0.00s)
PASS
ok  	example.com/hello
*/
func TestBytesAppend(t *testing.T) {
  var b []byte
  s := "Hello "
  b = append(b, "World!"...)
  t.Log(string(s))
}

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package hello

import "testing"

/*
=== RUN   TestStringCopy
    /Users/xxx/Codes/go/src/github.com/xxx/hello/hello_test.go:18: Hello World!
--- PASS: TestStringCopy (0.00s)
PASS
ok  	example.com/hello	(cached)
*/
func TestStringCopy(t *testing.T) {
  b := make([]byte, 0)
  b = mycopy(b, "Hello ")
  b = mycopy(b, "World!")
  t.Log(string(b))
}

func mycopy(b []byte, s string) []byte {
  n := len(b)
  if n+len(s) > cap(b) {
    t := make([]byte, 2*cap(b)+len(s))
    copy(t, b)
    b = t
  }
  b = b[0 : n+len(s)]
  copy(b[n:], s)
  return b
}

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package hello

import (
  "strings"
  "testing"
)

/*
=== RUN   TestStringBuilder
    /Users/xxx/Codes/go/src/github.com/xxx/hello/hello_test.go:20: Hello World!
--- PASS: TestStringBuilder (0.00s)
PASS
ok  	example.com/hello	0.013s
*/
func TestStringBuilder(t *testing.T) {
  var builder strings.Builder
  builder.WriteString("Hello ")
  builder.WriteString("World!")
  s := builder.String()
  t.Log(s)
}

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package hello

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

const (
  src = "Hello World!"
  cnt = 10000
)

var expected = strings.Repeat(src, cnt)

func mycopy(b []byte, s string) []byte {
  n := len(b)
  if n+len(s) > cap(b) {
    t := make([]byte, 2*cap(b)+len(s))
    copy(t, b)
    b = t
  }
  b = b[0 : n+len(s)]
  copy(b[n:], s)
  return b
}

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

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

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

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

func BenchmarkBytesAppend(b *testing.B) {
  var res string
  for n := 0; n < b.N; n++ {
    var bytes []byte
    for i := 0; i < cnt; i++ {
      bytes = append(bytes, src...)
    }
    res = string(bytes)
  }
  b.StopTimer()
  if res != expected {
    b.Errorf("got=%s, want=%s", string(res), expected)
  }
}

func BenchmarkStringCopy(b *testing.B) {
  var res 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++ {
      data = mycopy(data, src)
    }
    res = string(data)
  }
  b.StopTimer()
  if res != expected {
      b.Errorf("got=%s, want=%s", string(res), expected)
  }
}

func BenchmarkStringCopy2(b *testing.B) {
  var res string
  for n := 0; n < b.N; n++ {
    b := make([]byte, 0, 64) // same size as bootstrap array of bytes.Buffer
    for i := 0; i < cnt; i++ {
      l := len(b)
      if l+len(src) > cap(b) {
        t := make([]byte, 2*cap(b)+len(src))
        copy(t, b)
        b = t
      }
      b = b[0 : l+len(src)]
      copy(b[l:], src)
    }
    res = string(b)
  }
  b.StopTimer()
  if res != expected {
    b.Errorf("got=%s, want=%s", string(res), expected)
  }
}

func BenchmarkStringBuilder(b *testing.B) {
  var res string
  for n := 0; n < b.N; n++ {
    var builder strings.Builder
    for i := 0; i < cnt; i++ {
      builder.WriteString(src)
    }
    res = builder.String()
  }
  b.StopTimer()
  if res != expected {
    b.Errorf("got=%s, want=%s", string(res), expected)
  }
}

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$ go test -v -benchmem -run=^$ -bench '^(BenchmarkStringConcat|BenchmarkStringSprintf|BenchmarkStringJoin|BenchmarkBufferWrite|BenchmarkBytesAppend|BenchmarkStringCopy|BenchmarkStringCopy2|BenchmarkStringBuilder)$' example.com/hello
goos: darwin
goarch: amd64
pkg: example.com/hello
cpu: Intel(R) Core(TM) i5-5257U CPU @ 2.70GHz
BenchmarkStringConcat
BenchmarkStringConcat-4                8         131090517 ns/op        632845121 B/op     10004 allocs/op
BenchmarkStringSprintf
BenchmarkStringSprintf-4               4         295268326 ns/op        1075561174 B/op    29686 allocs/op
BenchmarkStringJoin
BenchmarkStringJoin-4                  6         287073860 ns/op        632845282 B/op     10008 allocs/op
BenchmarkBufferWrite
BenchmarkBufferWrite-4              5631            210591 ns/op          441616 B/op         13 allocs/op
BenchmarkBytesAppend
BenchmarkBytesAppend-4              7819            152409 ns/op          628720 B/op         25 allocs/op
BenchmarkStringCopy
BenchmarkStringCopy-4               8820            118761 ns/op          441552 B/op         12 allocs/op
BenchmarkStringCopy2
BenchmarkStringCopy2-4              9598            135427 ns/op          441552 B/op         12 allocs/op
BenchmarkStringBuilder
BenchmarkStringBuilder-4            7729            156815 ns/op          505840 B/op         24 allocs/op
PASS
ok      example.com/hello       17.512s