Suspension
(other/suspension.cpp)

• View this file on GitHub
• Last update: 2020-03-15 18:29:46+09:00
• Link: https://www.cs.cmu.edu/~rwh/theses/okasaki.pdf

Required by

• Banker's Queue (data_structure/bankers_queue.cpp)
• Physicist's Queue (data_structure/physicists_queue.cpp)
• Realtime Queue (data_structure/realtime_queue.cpp)
• Stream (data_structure/stream.cpp)

Verified with

• test/bankers_queue.test.cpp
• test/physicists_queue.test.cpp
• test/realtime_queue.test.cpp

Code

#include <functional>
#include <memory>
#include <utility>
#include <variant>

template <class T>
class suspension
    : private std::shared_ptr<std::variant<T, std::function<T()>>> {
public:
  using value_type = T;
  using func_type = std::function<T()>;
  using node_type = std::variant<T, func_type>;

private:
  using base_type = std::shared_ptr<node_type>;

  static T get(node_type &x) {
    if (x.index() != 0)
      x = std::get<1>(x)();
    return std::get<0>(x);
  }

  template <class... Args> static base_type make_node(Args &&... args) {
    return std::make_shared<node_type>(std::forward<Args>(args)...);
  }

public:
  suspension(std::in_place_t, T x)
      : base_type(make_node(std::in_place_index<0>, x)) {}

  suspension(func_type f) : base_type(make_node(std::in_place_index<1>, f)) {}

  T force() const { return get(**this); }
};

/**
 * @brief Suspension
 * @see https://www.cs.cmu.edu/~rwh/theses/okasaki.pdf
 */

#line 1 "other/suspension.cpp"
#include <functional>
#include <memory>
#include <utility>
#include <variant>

template <class T>
class suspension
    : private std::shared_ptr<std::variant<T, std::function<T()>>> {
public:
  using value_type = T;
  using func_type = std::function<T()>;
  using node_type = std::variant<T, func_type>;

private:
  using base_type = std::shared_ptr<node_type>;

  static T get(node_type &x) {
    if (x.index() != 0)
      x = std::get<1>(x)();
    return std::get<0>(x);
  }

  template <class... Args> static base_type make_node(Args &&... args) {
    return std::make_shared<node_type>(std::forward<Args>(args)...);
  }

public:
  suspension(std::in_place_t, T x)
      : base_type(make_node(std::in_place_index<0>, x)) {}

  suspension(func_type f) : base_type(make_node(std::in_place_index<1>, f)) {}

  T force() const { return get(**this); }
};

/**
 * @brief Suspension
 * @see https://www.cs.cmu.edu/~rwh/theses/okasaki.pdf
 */

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