Strings & Runes

# Why Strings and Runes Matter

Text bugs in production often come from assuming one character equals one byte. In Go, strings are UTF-8 byte sequences, so correctness requires understanding bytes, runes, and Unicode-safe iteration.

This matters for usernames, search, validation, and analytics where non-ASCII input is common.

# Strings Are Byte Sequences

len(s) returns bytes. Indexing returns a byte. Use range to decode Unicode code points.

s := "Hello, 世界"

fmt.Println(len(s))      // bytes
fmt.Println(s[0])        // byte

for i, r := range s {
    fmt.Printf("byte[%d]: %c
", i, r)
}

# Runes and Unicode Safety

A rune is an int32 Unicode code point. When input can contain emoji or CJK, operate on rune slices for semantic character operations (like reverse/palindrome).

r := '🎉'
fmt.Printf("%c %d
", r, r)

s := "こんにちは"
fmt.Println(len(s))        // bytes
fmt.Println(len([]rune(s))) // characters

# Efficient String Construction

For incremental building, prefer strings.Builder. For existing slices of strings, strings.Join is concise and efficient.

var b strings.Builder
for _, w := range []string{"go", "is", "fast"} {
    b.WriteString(w)
    b.WriteByte(' ')
}
fmt.Println(b.String())

# Practice Challenge

Implement IsPalindrome(s string) bool using runes, not bytes, so it works for multi-byte Unicode characters.

package main

import "fmt"

func IsPalindrome(s string) bool {
    // TODO: work correctly with multi-byte runes
}

func main() {
    fmt.Println(IsPalindrome("racecar"))
    fmt.Println(IsPalindrome("level"))
    fmt.Println(IsPalindrome("hello"))
}