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Simplify traversal_common.hpp by unifying property function concepts #22

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Merged
pratzl merged 1 commit into from
Apr 11, 2026
Merged

Simplify traversal_common.hpp by unifying property function concepts #22

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47 changes: 22 additions & 25 deletions include/graph/algorithm/traversal_common.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -115,6 +115,20 @@ constexpr auto zero_distance() {
return DistanceValue();
}

/// General concept: a callable returning a mutable lvalue reference to any per-vertex property value.
/// Used by connected_components, label_propagation, and similar algorithms with per-vertex
/// property output parameters.
template <class VF, class G>
concept vertex_property_fn_for =
std::invocable<VF&, const std::remove_reference_t<G>&, const vertex_id_t<G>&> &&
std::is_lvalue_reference_v<
std::invoke_result_t<VF&, const std::remove_reference_t<G>&, const vertex_id_t<G>&>>;

/// Type alias: extracts the value type from a vertex property function's return type
template <class VF, class G>
using vertex_fn_value_t = std::remove_cvref_t<
std::invoke_result_t<VF&, const std::remove_reference_t<G>&, const vertex_id_t<G>&>>;

//
// Distance and predecessor function concepts
//
Expand All @@ -124,38 +138,21 @@ constexpr auto zero_distance() {
// or in an external container.
//

/// Type alias: extracts the distance value type from a distance function's return type
/// Concept: a callable returning a mutable reference to a per-vertex distance value
template <class DF, class G>
using distance_fn_value_t = std::remove_cvref_t<
std::invoke_result_t<DF&, const std::remove_reference_t<G>&, const vertex_id_t<G>&>>;
concept distance_fn_for = vertex_property_fn_for<DF, G>;

/// Concept: a callable returning a mutable reference to a per-vertex distance value
/// Type alias: extracts the distance value type from a distance function's return type
template <class DF, class G>
concept distance_fn_for =
std::invocable<DF&, const std::remove_reference_t<G>&, const vertex_id_t<G>&> &&
std::is_lvalue_reference_v<
std::invoke_result_t<DF&, const std::remove_reference_t<G>&, const vertex_id_t<G>&>>;
using distance_fn_value_t = vertex_fn_value_t<DF, G>;

/// Type alias: extracts the predecessor value type from a predecessor function's return type
/// Concept: a callable returning a mutable reference to a per-vertex predecessor value
template <class PF, class G>
concept predecessor_fn_for =
std::invocable<PF&, const std::remove_reference_t<G>&, const vertex_id_t<G>&> &&
std::is_lvalue_reference_v<
std::invoke_result_t<PF&, const std::remove_reference_t<G>&, const vertex_id_t<G>&>>;
concept predecessor_fn_for = vertex_property_fn_for<PF, G>;

/// General concept: a callable returning a mutable lvalue reference to any per-vertex property value.
/// Used by connected_components, label_propagation, and similar algorithms with per-vertex
/// property output parameters.
template <class VF, class G>
concept vertex_property_fn_for =
std::invocable<VF&, const std::remove_reference_t<G>&, const vertex_id_t<G>&> &&
std::is_lvalue_reference_v<
std::invoke_result_t<VF&, const std::remove_reference_t<G>&, const vertex_id_t<G>&>>;

/// Type alias: extracts the value type from a vertex property function's return type
template <class VF, class G>
using vertex_fn_value_t = std::remove_cvref_t<
std::invoke_result_t<VF&, const std::remove_reference_t<G>&, const vertex_id_t<G>&>>;
template <class PF, class G>
using predecessor_fn_value_t = vertex_fn_value_t<PF, G>;

/// Null predecessor function — used when predecessor tracking is not needed.
/// Detected at compile time via is_null_predecessor_fn_v to skip predecessor writes.
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