Invercargill/src/lib/Collections/Collection.vala

namespace Invercargill {

    public abstract class Collection<T> : Enumerable<T> {

        public abstract void add(T item);
        public abstract void remove_first_where(PredicateDelegate<T> predicate);
        public abstract void remove_where(PredicateDelegate<T> predicate);

        public virtual void add_all(Enumerable<T> items) {
            items.iterate(i => add(i));
        }

    }

    public abstract class IndexedCollection<T> : Collection<T> {

        public new abstract T @get(int index) throws IndexError;
        public new abstract void @set(int index, T item) throws IndexError;
        public abstract void remove(int index) throws IndexError;
        public abstract int index_of(PredicateDelegate<T> predicate);

    }
    
}