Empty a collection and reuse its storage

Lists, dictionaries, and sets have clear() -> (). The method requires mutable access, drops the contents, and retains capacity for later insertions:

def main() -> Result[(), AllocError | IoError]:
    mut items = [10, 20]?
    items.clear()
    print(items)?
    items.append(30)?
    print(items)?
    mut scores = {"Ada": 10}?
    scores.clear()
    print(scores)?
    Ok(())

[]
[30]
{}

Clearing itself allocates no storage. Owned elements are destroyed before the method returns, in list order or dictionary insertion order; custom destructors may have their own effects and allocations. Clearing an empty collection is fine.