Return type of read-only getter (tools/getter_result.hpp)

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• Last update: 2025-12-14 14:57:31+09:00
• Include: #include "tools/getter_result.hpp"

template <typename T, typename U>
struct getter_result {
  using type = std::conditional_t<std::is_lvalue_reference_v<T>, const U&, U>;
};

template <typename T, typename U>
using getter_result_t = typename getter_result<T, U>::type;

tools::getter_result is a small type trait that helps you choose an appropriate return type for “getter”-like functions depending on whether the object (this) is an lvalue or an rvalue.

It is especially useful in C++23-style explicit object parameter member functions, e.g.:

auto edges(this auto&& self) -> tools::getter_result_t<decltype(self), std::vector<edge>> {
  return std::forward_like<decltype(self)>(self.m_edges);
}

With tools::getter_result, you can write a single getter that:

• returns const U& when called on an lvalue object, and
• returns U by value when called on an rvalue object.

This allows efficient move (or copy) of the member from temporary objects, while preventing modification through getters on lvalues.

Constraints

• None

Time Complexity

• Not applicable

License

• CC0

Author

• anqooqie

Required by

• Bellman-Ford algorithm (tools/bellman_ford.hpp)
• Arbitrary precision floating-point number (tools/bigdecimal.hpp)
• Matching on bipartite graph (tools/bipartite_matching.hpp)
• Cartesian tree (tools/cartesian_tree.hpp)
• Two-dimensional circle (tools/circle_2d.hpp)
• Two-dimensional circumcircle (tools/circumcircle_2d.hpp)
• Cycle detection on a graph (tools/cycle_detection.hpp)
• tools/detail/geometry_2d.hpp
• Dijkstra's algorithm (tools/dijkstra.hpp)
• Two-dimensional directed line segment (tools/directed_line_segment_2d.hpp)
• List all divisors of a divisor of $n$ (tools/divisors_of_divisor.hpp)
• Two-dimensional half line (tools/half_line_2d.hpp)
• Check whether a given graph is bipartite (tools/is_bipartite.hpp)
• Two-dimensional line (tools/line_2d.hpp)
• Dijkstra's algorithm for dense graph (tools/naive_dijkstra.hpp)
• Two-dimensional polygon (tools/polygon_2d.hpp)
• Prim's algorithm (tools/prim.hpp)
• Rational number (tools/rational.hpp)
• Shortest path tree (tools/shortest_path_tree.hpp)
• Two-dimensional triangle (tools/triangle_2d.hpp)
• Topological sorting (tools/tsort.hpp)
• Traveling salesman problem (tools/tsp.hpp)
• Matching on weighted bipartite graph (tools/weighted_bipartite_matching.hpp)
• 01-BFS (tools/zero_one_bfs.hpp)

Verified with

• tests/bellman_ford.test.cpp
• tests/bigdecimal/cast_to_long_long.test.cpp
• tests/bigdecimal/divides.test.cpp
• tests/bigdecimal/hand.test.cpp
• tests/bigdecimal/minus.test.cpp
• tests/bigdecimal/multiplies.test.cpp
• tests/bigdecimal/plus.test.cpp
• tests/bigdecimal/random.test.cpp
• tests/bigdecimal/rounding.test.cpp
• tests/bipartite_matching.test.cpp
• tests/cartesian_tree/parent.test.cpp
• tests/cartesian_tree/tree_based_interval.test.cpp
• tests/cartesian_tree/value_based_interval.test.cpp
• tests/circle_2d/intersection_to_circle.test.cpp
• tests/circle_2d/intersection_to_line.test.cpp
• tests/circle_2d/where/with_radius.test.cpp
• tests/circle_2d/where/without_radius.test.cpp
• tests/cycle_detection/directed.test.cpp
• tests/cycle_detection/undirected.test.cpp
• tests/dijkstra/directed.test.cpp
• tests/dijkstra/undirected.test.cpp
• tests/directed_line_segment_2d/cross_point.test.cpp
• tests/directed_line_segment_2d/crosses.test.cpp
• tests/directed_line_segment_2d/intersection.test.cpp
• tests/directed_line_segment_2d/squared_distance.test.cpp
• tests/divisors_of_divisor.test.cpp
• tests/getter_result.test.cpp
• tests/groups.test.cpp
• tests/is_bipartite.test.cpp
• tests/line_2d/is_parallel_to.test.cpp
• tests/line_2d/projection.test.cpp
• tests/naive_dijkstra.test.cpp
• tests/polygon_2d/area.test.cpp
• tests/polygon_2d/minimum_bounding_circle.test.cpp
• tests/polygon_2d/where.test.cpp
• tests/prim/basic.test.cpp
• tests/prim/unconnected.test.cpp
• tests/rational/minus.test.cpp
• tests/rational/multiplies.test.cpp
• tests/rational/plus.test.cpp
• tests/rational/random.test.cpp
• tests/triangle_2d/circumcircle/double.test.cpp
• tests/triangle_2d/circumcircle/rational.test.cpp
• tests/triangle_2d/incircle.test.cpp
• tests/tsort/count.test.cpp
• tests/tsort/query.test.cpp
• tests/tsp.test.cpp
• tests/weighted_bipartite_matching/maximize.test.cpp
• tests/weighted_bipartite_matching/minimize.test.cpp
• tests/weighted_bipartite_matching/multiple_calls.test.cpp
• tests/zero_one_bfs/directed.test.cpp
• tests/zero_one_bfs/undirected.test.cpp

Code

#ifndef TOOLS_GETTER_RESULT_HPP
#define TOOLS_GETTER_RESULT_HPP

#include <type_traits>

namespace tools {
  template <typename T, typename U>
  struct getter_result {
    using type = std::conditional_t<std::is_lvalue_reference_v<T>, const U&, U>;
  };

  template <typename T, typename U>
  using getter_result_t = typename tools::getter_result<T, U>::type;
}

#endif

#line 1 "tools/getter_result.hpp"



#include <type_traits>

namespace tools {
  template <typename T, typename U>
  struct getter_result {
    using type = std::conditional_t<std::is_lvalue_reference_v<T>, const U&, U>;
  };

  template <typename T, typename U>
  using getter_result_t = typename tools::getter_result<T, U>::type;
}

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