Invercargill/src/lib/Interfaces/ReadOnlyAssociative.vala

namespace Invercargill {

    [GenericAccessors]
    public interface ReadOnlyAssociative<TKey, TValue> : Lot<KeyValuePair<TKey, TValue>> {

        public abstract bool try_get(TKey key, out TValue value);
        public abstract bool has(TKey key);
        public abstract Enumerable<TKey> keys { owned get; }
        public abstract Enumerable<TValue> values { owned get; }

        public virtual TValue @get(TKey key) throws IndexError {
            TValue value;
            if(try_get(key, out value)) {
                return value;
            }
            throw new IndexError.KEY_NOT_FOUND(@"Key not found in the associative collection");
        }
        
        public virtual TValue? get_or_default(TKey key) {
            TValue value;
            if(try_get(key, out value)) {
                return value;
            }
            return null;
        }

    }
}