Custom Collection Types


Collections can also hold [`Dynamic`] values (e.g. like an [array]).

A collection type holds a… well… collection of items. It can be homogeneous (all items are the same type) or heterogeneous (items are of different types, use Dynamic to hold).

Because their only purpose for existence is to hold a number of items, collection types commonly register the following methods.

Method	Description
`len` method and property	gets the total number of items in the collection
`clear`	clears the collection
`contains`	checks if a particular item exists in the collection
`add`, `+=` operator	adds a particular item to the collection
`remove`, `-=` operator	removes a particular item from the collection
`merge` or `+` operator	merges two collections, yielding a new collection with all items


Collections are typically iterable.

It is customary to use `Engine::register_iterator` to allow iterating the collection if
it implements `IntoIterator`.

Alternative, register a specific [type iterator] for the [custom type].


A [plugin module] makes defining an entire API for a [custom type] a snap.

Example

type MyBag = HashSet<MyItem>;

engine
    .register_type_with_name::<MyBag>("MyBag")
    .register_iterator::<MyBag>()
    .register_fn("new_bag", || MyBag::new())
    .register_fn("len", |col: &mut MyBag| col.len() as i64)
    .register_get("len", |col: &mut MyBag| col.len() as i64)
    .register_fn("clear", |col: &mut MyBag| col.clear())
    .register_fn("contains", |col: &mut MyBag, item: i64| col.contains(&item))
    .register_fn("add", |col: &mut MyBag, item: MyItem| col.insert(item))
    .register_fn("+=", |col: &mut MyBag, item: MyItem| col.insert(item))
    .register_fn("remove", |col: &mut MyBag, item: MyItem| col.remove(&item))
    .register_fn("-=", |col: &mut MyBag, item: MyItem| col.remove(&item))
    .register_fn("+", |mut col1: MyBag, col2: MyBag| {
        col1.extend(col2.into_iter());
        col1
    });