Invercargill/src/lib/Modifiers/From.vala

namespace Invercargill.Modifiers {

    public class From<T> : Enumerable<T> {
        private Enumerable<T> input;
        private PredicateDelegate<T> predicate_func;

        public From(Enumerable<T> input, owned PredicateDelegate<T> func) {
            this.input = input;
            predicate_func = (owned)func;
        }

        public override uint? peek_count() {
            return null;
        }

        public override EnumerableInfo get_info() {
            return new EnumerableInfo.infer_single(this, EnumerableCategory.COMPUTED, input);
        }

        public override Tracker<T> get_tracker() {
            var tracker = input.get_tracker();
            var condition_met = false;

            return new AdvanceTracker<T>((out obj) => {
                obj = null;
                do {
                    if(!tracker.has_next()) {
                        obj = null;
                        return false;
                    }
                    obj = tracker.get_next ();
                } while(!condition_met && !predicate_func(obj));
                condition_met = true;
                return true;
            });
        }
    }

}