WeakSingleton.h

#ifndef PROFILER_SRC_MOLPRO_PROFILER_TREE_SINGLE_H
#define PROFILER_SRC_MOLPRO_PROFILER_TREE_SINGLE_H
#include <algorithm>
#include <cassert>
#include <list>
#include <memory>
#include <string>
 
namespace molpro {
namespace profiler {
  std::shared_ptr<Profiler> s_saver;
 
// FIXME improve description
template <class Object>
struct WeakSingleton {
 
  using key_t = std::tuple<std::string, std::weak_ptr<Object>, Object*>;
 
  template <typename... T>
  static std::shared_ptr<Object> single(const std::string& key, T&&... constructor_args) {
    std::shared_ptr<Object> result = nullptr;
    auto it =
        std::find_if(begin(m_register), end(m_register), [&key](const key_t& el) { return std::get<0>(el) == key; });
    if (it != m_register.end())
      result = std::get<1>(*it).lock();
    if (!result) {
      result = std::make_shared<Object>(std::forward<T>(constructor_args)...);
      m_register.emplace_back(key_t{key, result, result.get()});
    }
    return result;
  }
 
  static std::shared_ptr<Object> single() {
    if (m_register.empty() or not std::get<1>(m_register.back()).lock()) { // default zero-depth instance
      auto result = Profiler::single("default");
      result->set_max_depth(0);
      return result;
    }
    assert(!m_register.empty() && "First must make a call to single(key, ...) to create an object");
    std::shared_ptr<Object> result = std::get<1>(m_register.back()).lock();
    assert(result && "The last registered object was deallocated");
    return result;
  }
 
  static void erase(Object* obj) {
    auto it =
        std::find_if(begin(m_register), end(m_register), [obj](const key_t& el) { return std::get<2>(el) == obj; });
    if (it != m_register.end())
      m_register.erase(it);
  }
 
  static void erase(const std::string& key) {
    auto it =
        std::find_if(begin(m_register), end(m_register), [&key](const key_t& el) { return std::get<0>(el) == key; });
    if (it != m_register.end())
      m_register.erase(it);
  }
 
  static void clear() { m_register.clear(); }
 
  static std::list<key_t> m_register; 
};
 
} // namespace profiler
} // namespace molpro
#endif // PROFILER_SRC_MOLPRO_PROFILER_TREE_SINGLE_H