How to Join Strings in Go with strings.Join

Use the strings.Join function from the standard library to concatenate a slice of strings with a specific separator. It is the most efficient and idiomatic way to join strings in Go, avoiding the performance pitfalls of repeated string concatenation in loops.

Here is a basic example joining a slice of words with a space separator:

package main

import (
	"fmt"
	"strings"
)

func main() {
	words := []string{"Hello", "world", "from", "Go"}
	result := strings.Join(words, " ")
	fmt.Println(result) // Output: Hello world from Go
}

If you need to join strings with a newline or handle empty slices, strings.Join handles those cases gracefully. An empty separator results in direct concatenation, and an empty slice returns an empty string.

package main

import (
	"fmt"
	"strings"
)

func main() {
	lines := []string{"Line 1", "Line 2", "Line 3"}
	// Join with newlines
	output := strings.Join(lines, "\n")
	fmt.Println(output)

	// Join with empty separator (concatenation)
	tags := []string{"go", "backend", "api"}
	combined := strings.Join(tags, "")
	fmt.Println(combined) // Output: gobackendapi

	// Empty slice returns empty string
	empty := []string{}
	fmt.Println(len(strings.Join(empty, ","))) // Output: 0
}

Avoid manually looping and appending to a string variable, as strings are immutable in Go. That approach creates a new string object on every iteration, leading to O(n²) time complexity. strings.Join calculates the final size upfront and performs a single allocation, resulting in O(n) performance.

If you need to join strings with a custom format (e.g., adding quotes around each element), you should transform the slice first or use fmt.Sprintf for simple cases, but strings.Join remains the standard for pure concatenation with separators.

strings.Join takes a list of words and a separator, then glues them together into one string. It is the standard way to combine text items without writing a manual loop. Think of it like using a comma to join a list of names in a sentence.