Build text with recoverable allocation

Use text.concat(other) to combine two strings. To combine a list or another iterable of strings, use separator.join(parts). Both return Result[str, AllocError]:

def greeting(names: &list[str]) -> Result[str, AllocError]:
    joined = ", ".join(names)?
    "Hello, ".concat(joined)?.concat("!")

def main() -> Result[(), AllocError | IoError]:
    names = ["Ada", "Bea"]?
    print(greeting(&names)?)?
    print(names)?
    print("-".join([]?)?)?
    Ok(())

Hello, Ada, Bea!
["Ada", "Bea"]

The methods borrow their inputs. Joining first calculates the final size and then allocates one output buffer; it does not build a succession of intermediate strings. An empty list gives an empty string, and a one-element list adds no separator. Empty pieces still count: joining ["a", "", "b"] with "-" gives "a--b".

UTF-8 characters and embedded \0 are preserved. join also accepts a set, a dictionary (its keys), a string (its scalars), or a generator of strings; see building text for each form’s allocations.