Visitor extensions#31
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- Add has_any_visitor_event<G,V> — disjunction of all 19 has_on_* concepts
- Add valid_visitor<G,V> — satisfied by empty_visitor or any visitor with at
least one recognised on_* callback; rejects structs whose only on_*-like
methods are misspelled and would otherwise be silently ignored
- Add #include <concepts> and <type_traits> to traversal_common.hpp
- Enforce valid_visitor via static_assert at the top of the implementing body
of bfs, dfs, dijkstra and bellman_ford; message directs user to the typo
and the empty_visitor{} escape hatch
- Add compile-time static_assert tests in test_breadth_first_search.cpp
covering empty_visitor (pass), a correct visitor (pass), and a typo
visitor (fail)
BGL-style composable visitors built on the existing duck-typed on_* model, without changing any traversal algorithm. Layer 1 — single-event adaptors (on_discover_vertex(f), on_tree_edge(f), ...): wrap a callable so it fires for exactly one event; analogue of BGL event tags. Generated for all 14 event names (5 vertex + 9 edge) via a macro. Layer 2 — composite_visitor / make_visitor(...): fan one traversal out to many sub-visitors. Each event method is constrained by a fold over the child pack, so a composite only exposes on_X when a child handles X — keeping has_on_* and valid_visitor detection accurate and preserving zero-overhead event skipping. Bridges descriptor- and id-form children from a single event via vertex_id(). Layer 3 — prebuilt recorders: predecessor_recorder, distance_recorder (weighted + hop-count overloads) and time_stamper. Each returns a plain (g,x)->void callable so the caller binds it to any event, e.g. on_tree_edge(predecessor_recorder(pred)) for BFS/DFS or on_edge_relaxed(predecessor_recorder(pred)) for Dijkstra/Bellman-Ford. - Register header in graph/algorithms.hpp umbrella - Add tests/algorithms/test_visitor_factory.cpp (compile-time valid_visitor / has_on_* integration checks + runtime BFS/DFS/Dijkstra coverage) - Wire test file into tests/algorithms/CMakeLists.txt
…tegy.md visitor_factory.hpp: Add '@Par BGL Comparison' section to the file-level Doxygen block showing BGL make_bfs_visitor syntax vs. graph-v3 make_visitor, plus a bullet list of four key design differences. bgl_migration_strategy.md: Update Section 7 'Visitor Pattern Migration' to replace the 'Composable Visitor Adaptors — Gap (still open)' subsection with full documentation of the three-layer toolkit (single-event adaptors, make_visitor, prebuilt recorders), the BGL vs. graph-v3 syntax comparison, and a per-recorder event-binding table. Also update the Key Differences table, Executive Summary gaps list, Phase 3 roadmap table, and 'Done' note. Bump last-reviewed date to 2026-05-30.
…isitor_factory Local variable 'edges' at lines 75 and 92 shadowed graph::adj_list::_cpo_instances::edges (graph_cpo.hpp:816). Clang on macOS/CI treats -Wshadow as -Werror.
…extensions branch
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