Look up a character without trapping

Use text.get(index) when the index might be out of range. It returns Option[str]: Some(character) when the index exists, Nothing otherwise.

def show_character(text: &str, index: i64) -> Result[(), IoError]:
    match text.get(index):
        case Some(value):
            print(value)?
        case Nothing:
            print("missing")?
    Ok(())

def main() -> Result[(), IoError]:
    text = "café🙂"
    show_character(&text, -1)?
    show_character(&text, 3)?
    show_character(&text, 5)?
    print(text)?
    Ok(())

🙂
é
missing
café🙂

Indices are i64 and count Unicode scalars, as with text[index]. Negative indices count backward from the end; -1 selects the last scalar. Empty strings and indices outside either end return Nothing. Neither form allocates: a character is a short string stored inline in the value, independent of the original, which remains available.

Ordinary text[index] terminates the program for a missing index. Indexing ASCII text takes constant time; other text is scanned from the start to reach the requested scalar, so use for character in text to traverse it.