Complete work without returning data

A function can complete without producing data. Its return type is the unit type, (). This is different from a missing value.

def show_if(enabled: bool, value: i64) -> Result[(), IoError]:
    if not enabled:
        return Ok(())
    print(value)?
    Ok(())

def main() -> Result[(), IoError]:
    show_if(False, 10)?
    show_if(True, 42)?
    Ok(())

42

Result[(), IoError] combines unit success with a possible output error. print(value)? therefore completes without supplying data.

In a function declared -> (), a bare return returns unit. Use pass for an intentionally empty block. Unit parameters and standalone unit bindings are not supported. Use Option for absence; there is no None value.