Invercargill/src/lib/Cache.vala

namespace Invercargill {

    public delegate T CachedGet<T>();

    private static Dictionary<int, NativeElement> cache;

    public T once<T>(owned CachedGet<T> constructor) {
        if(cache == null) {
            cache = new Dictionary<int, NativeElement>();
        }

        int location = (int)constructor;
        NativeElement<T> element;
        if(!cache.try_get(location, out element)) {
            element = new NativeElement<T>(constructor());
            cache.set(location, element);
        }

        return element.assert_as<T>();
    }
}