Golang Pitfalls: Strings & Bytes

Source material: mistakes #36-41 from 100 Go Mistakes and How to Avoid Them (teivah/100-go-mistakes).

Apply these rules when manipulating strings in Go.

36. Not understanding the concept of rune (#36)

• A charset is a set of characters; an encoding translates characters to binary.
• A Go string references an immutable slice of arbitrary bytes. Source-code literals are UTF-8, but strings from elsewhere may not be.
• A rune is a Unicode code point, encoded in UTF-8 using 1 to 4 bytes.
• len(s) returns the number of bytes, not runes. ("hêllo" has 5 runes but len == 6.)

37. Inaccurate string iteration (#37)

• for i := range s iterates over the starting byte index of each rune, not each rune.
• s[i] returns a single byte — printing it corrupts multi-byte runes (e.g., ê prints as Ã).
• To print all runes, use the value element: for i, r := range s { ... }.
• To access the ith rune, convert to []rune: []rune(s)[i]. This conversion costs O(n) — avoid it in hot loops; prefer range with the value when iterating everything.