Keep distinct values in a set

A set[T] stores each distinct value once. Its elements can be integers, booleans, or strings:

def main() -> Result[(), AllocError | IoError]:
    mut names: set[str] = set()?
    names.add("Ada")?
    names.add("Ada")?
    print(len(names))?
    print("Ada" in names)?
    names.add("Grace")?
    print(names.discard("Ada"))?
    print(names.discard("Ada"))?
    print(len(names))?
    Ok(())

1
True
True
False
1

add needs mutable access and returns an allocation result. discard removes a member without allocating and returns whether it was present.

Use set[str]()? for a typed empty set, or provide an annotation as above. A display such as {"Ada", "Grace"}? builds a set directly. {} is an empty dictionary. Sets have no promised iteration order.

Dictionary and set equality compare contents independently of order.