pipelineDECL pipelineC::iterator pipelineC::begin() {
    pipeline *_;
    for(_ = this; _->_prev != NULL; _ = _->_prev);
    return iterator(_->_iter_head);
}

pipelineDECL pipelineC::iterator pipelineC::end() {
    pipeline *_;
    for(_ = this; _->_next != NULL; _ = _->_next);
    return iterator(_);
}