.. _cpp-invariant/coordinator:

**********************************************************
coordinator.hpp
**********************************************************

Full path: ``graph_canon/invariant/coordinator.hpp``

.. default-domain:: cpp
.. default-role:: cpp:expr

.. cpp:namespace:: graph_canon

.. class:: invariant_coordinator

    A visitor for properly coordinating multiple node invariants.
    That is, ensuring a total order among different providers.

    .. function:: template<typename State> \
                  static std::size_t init_visitor(State &state)

        Must be called by each node invariant visitor, probably in its `initialize` method.

        :returns: an ID that must be provided in subsequent calls to the coordinator.
    .. function:: template<typename State, typename TreeNode> \
                  static bool add_invariant_element(State &state, TreeNode &t, const std::size_t visitor)

        Tell the coordinator that the calling visitor wants to add another trace element.
        This may fail if another visitor has the current invariant position.

        :returns: `true` if the calling visitor may add a value, `false` if not.
    .. function:: template<typename State, typename TreeNode> \
                  static void better_invariant(State &state, TreeNode &t)

        Must be called by a visitor when it has been allowed to add a value,
        and that value is better than the value the visitor previously had in this position.

        Will invoke the `invariant_better` event and prune the current best leaf.
    .. function:: template<typename State, typename TreeNode> \
                  static void worse_invariant(State &state, TreeNode &t)

        Must be called by a visitor when it has been allowed to add a value,
        but that value is worse than the value the visitor previously had in this position.

        Currently this method does nothing.