A common mistake is concatenating a slice of strings with += inside a loop and overlooking string immutability. Each iteration reallocates a new string and copies content, so the function can become significantly slower as the result grows. section 5.4
func concat(values []string) string {
s := ""
for _, value := range values {
s += value
}
return s
}
This implementation is simple and correct, but repeatedly reallocates the result during the loop. section 5.4
Use strings.Builder when joining many strings. Its WriteString method appends data to an internal buffer, minimizing memory copying; Write, WriteByte, and WriteRune support other input forms. The ignored error is intentional because WriteString does not return a non-nil error, while its signature satisfies io.StringWriter. section 5.4
func concat(values []string) string {
sb := strings.Builder{} #1
for _, value := range values {
_, _ = sb.WriteString(value) #2
}
return sb.String() #3
}
This version builds the result with strings.Builder and returns the completed value with String. section 5.4
Choose the implementation according to the workload:
- Call Grow when the total byte length is known. Preallocating the builder reduces additional growth and can improve performance. section 5.4
- Do not use one strings.Builder concurrently: its internal byte slice is appended to during writes, so concurrent calls can race. section 5.4
- Benchmarks show the += version at 72,291,485 ns/op, the basic Builder version at 878,962 ns/op, and the Grow version at 190,340 ns/op. section 5.4
