Go Builder
last modified August 24, 2023
Go Builder tutorial shows how to build strings efficiently in Golang with strings.Builder.
We build a string with various write methods such as WriteString
or WriteRune. In the end, we return the accumulated string with
the String method.
The Builder uses an internal slice to store data.
$ go version go version go1.18.1 linux/amd64
We use Go version 1.18.
Go Builder example
The next example uses the strings.Builder to form a message.
package main
import (
"fmt"
"strings"
)
func main() {
builder := strings.Builder{}
builder.WriteString("There")
builder.WriteString(" are")
builder.WriteString(" three")
builder.WriteString(" hawks")
builder.WriteString(" in the sky")
fmt.Println(builder.String())
}
We build a message using Builder's WriteString.
$ go run simple.go There are three hawks in the sky
The next example builds a string from byte slices.
package main
import (
"fmt"
"strings"
)
func main() {
builder := strings.Builder{}
data1 := []byte{72, 101, 108, 108, 111}
data2 := []byte{32}
data3 := []byte{116, 104, 101, 114, 101, 33}
builder.Write(data1)
builder.Write(data2)
builder.Write(data3)
fmt.Println(builder.String())
}
The example builds a string with Write.
$ go run simple2.go Hello there!
Go Builder - building formatted strings
In the next example, we build a formatted string.
package main
import (
"fmt"
"strings"
)
func main() {
builder := strings.Builder{}
animals := "hawks"
n := 3
builder.WriteString("There are ")
builder.WriteString(fmt.Sprintf("%d %s ", n, animals))
builder.WriteString("in the sky.")
msg := builder.String()
fmt.Println(msg)
}
We use the fmt.Sprintf function to create a formatted string and
append it to the builder with WriteString.
Go Builder - comparing performance
In the next example, we compare the performance of a Builder
against a string concatenation with the + operator.
package main
import (
"fmt"
"strings"
"time"
)
func main() {
t0 := time.Now()
builder := strings.Builder{}
for i := 0; i < 100_000; i++ {
builder.WriteString("falcon")
}
t1 := time.Now()
result := ""
for i := 0; i < 100_000; i++ {
result += "falcon"
}
t2 := time.Now()
fmt.Println(t1.Sub(t0))
fmt.Println(t2.Sub(t1))
}
The example benchmarks the efficiency of the two ways of string concatenation; it adds the word falcon hundred thousad times.
$ go run compare.go 2.232505ms 8.007376273s
As we can see from the output, the Builder is much more efficient.
In this article we have worked with the strings.Builder in Go.
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