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Learn Data Structures and Algorithms in Go

String Immutability

Explore the concept of string immutability in Go and understand the fundamental difference between strings and slices. Learn why strings cannot be modified in place, how new strings are created instead, and how this impacts the design and efficiency of string algorithms in Go programming.

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By this point, you know that individual characters in strings can be accessed and traversed, and the length of a string can be determined using the same ideas that apply to arrays and slices. That structural similarity makes strings feel familiar. However, there is one place where strings and arrays or slices part ways in a significant and consequential manner, and it shows up the moment any attempt is made to modify a string. Understanding this difference is not just a matter of knowing a language rule. It directly affects how string algorithms are designed, how their performance is analyzed, and why certain patterns appear in string code again and again.

Attempting to modify a string

Consider a simple slice of integers. Changing the first element is a straightforward operation where the value at that position is simply overwritten.

Go (1.24.2)
package main
import "fmt"
func main() {
	arr := []int{1, 2, 3, 4, 5}
	arr[0] = 99
	fmt.Println(arr) // [99 2 3 4 5]
}

Now consider trying to do the same thing with a string.

Go (1.24.2)
package main
func main() {
	s := "hello"
	s[0] = 'H' // compile-time error: cannot assign to s[0]
}

The error shows that a character in a string cannot be replaced in the same ...