Remove set members

Use values.discard(value) to remove a member from a mutable set. It returns True if the member was present and removed, or False if it was absent:

def main() -> Result[(), AllocError | IoError]:
    mut names = {"Ada", "Bea"}?
    name = "Ada"
    print(names.discard(name))?
    print(names.discard(name))?
    print(name)?
    print("Bea" in names)?
    print(len(names))?
    names.add(name)?
    print(len(names))?
    Ok(())

True
False
Ada
True
1
2

The argument is observed, so name remains usable. Discarding a stored zero, False, or empty string still returns True. Removal allocates nothing and preserves capacity for reuse. Like dictionary removal, it has expected constant cost for well-distributed keys, apart from hashing and cleanup; heavy hash collisions can still slow it down. Use an exclusive reference when removing members through a function parameter.