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.

len method and propertygets the total number of items in the collection
clearclears the collection
containschecks if a particular item exists in the collection
add, += operatoradds a particular item to the collection
remove, -= operatorremoves a particular item from the collection
merge or + operatormerges two collections, yielding a new collection with all items

Tip: Define type iterator

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.

Tip: Use a plugin module

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


type MyBag = HashSet<MyItem>;

    .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| {