text: /*
      pybind11/detail/init.h: init factory function implementation and support code.
  
      Copyright (c) 2017 Jason Rhinelander <jason@imaginary.ca>
  
      All rights reserved. Use of this source code is governed by a
      BSD-style license that can be found in the LICENSE file.
  */
  
  #pragma once
  
  #include "class.h"
  
  PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
  PYBIND11_NAMESPACE_BEGIN(detail)
  
  template <>
  class type_caster<value_and_holder> {
  public:
      bool load(handle h, bool) {
          value = reinterpret_cast<value_and_holder *>(h.ptr());
          return true;
      }
  
      template <typename> using cast_op_type = value_and_holder &;
      operator value_and_holder &() { return *value; }
      static constexpr auto name = _<value_and_holder>();
  
  private:
      value_and_holder *value = nullptr;
  };
  
  PYBIND11_NAMESPACE_BEGIN(initimpl)
  
  inline void no_nullptr(void *ptr) {
      if (!ptr) throw type_error("pybind11::init(): factory function returned nullptr");
  }
  
  // Implementing functions for all forms of py::init<...> and py::init(...)
  template <typename Class> using Cpp = typename Class::type;
  template <typename Class> using Alias = typename Class::type_alias;
  template <typename Class> using Holder = typename Class::holder_type;
  
  template <typename Class> using is_alias_constructible = std::is_constructible<Alias<Class>, Cpp<Class> &&>;
  
  // Takes a Cpp pointer and returns true if it actually is a polymorphic Alias instance.
  template <typename Class, enable_if_t<Class::has_alias, int> = 0>
  bool is_alias(Cpp<Class> *ptr) {
      return dynamic_cast<Alias<Class> *>(ptr) != nullptr;
  }
  // Failing fallback version of the above for a no-alias class (always returns false)
  template <typename /*Class*/>
  constexpr bool is_alias(void *) { return false; }
  
  // Constructs and returns a new object; if the given arguments don't map to a constructor, we fall
  // back to brace aggregate initiailization so that for aggregate initialization can be used with
  // py::init, e.g.  `py::init<int, int>` to initialize a `struct T { int a; int b; }`.  For
  // non-aggregate types, we need to use an ordinary T(...) constructor (invoking as `T{...}` usually
  // works, but will not do the expected thing when `T` has an `initializer_list<T>` constructor).
  template <typename Class, typename... Args, detail::enable_if_t<std::is_constructible<Class, Args...>::value, int> = 0>
  inline Class *construct_or_initialize(Args &&...args) { return new Class(std::forward<Args>(args)...); }
  template <typename Class, typename... Args, detail::enable_if_t<!std::is_constructible<Class, Args...>::value, int> = 0>
  inline Class *construct_or_initialize(Args &&...args) { return new Class{std::forward<Args>(args)...}; }
  
  // Attempts to constructs an alias using a `Alias(Cpp &&)` constructor.  This allows types with
  // an alias to provide only a single Cpp factory function as long as the Alias can be
  // constructed from an rvalue reference of the base Cpp type.  This means that Alias classes
  // can, when appropriate, simply define a `Alias(Cpp &&)` constructor rather than needing to
  // inherit all the base class constructors.
  template <typename Class>
  void construct_alias_from_cpp(std::true_type /*is_alias_constructible*/,
                                value_and_holder &v_h, Cpp<Class> &&base) {
      v_h.value_ptr() = new Alias<Class>(std::move(base));
  }
  template <typename Class>
  [[noreturn]] void construct_alias_from_cpp(std::false_type /*!is_alias_constructible*/,
                                             value_and_holder &, Cpp<Class> &&) {
      throw type_error("pybind11::init(): unable to convert returned instance to required "
                       "alias class: no `Alias<Class>(Class &&)` constructor available");
  }
  
  // Error-generating fallback for factories that don't match one of the below construction
  // mechanisms.
  template <typename Class>
  void construct(...) {
      static_assert(!std::is_same<Class, Class>::value /* always false */,
              "pybind11::init(): init function must return a compatible pointer, "
              "holder, or value");
  }
  
  // Pointer return v1: the factory function returns a class pointer for a registered class.
  // If we don't need an alias (because this class doesn't have one, or because the final type is
  // inherited on the Python side) we can simply take over ownership.  Otherwise we need to try to
  // construct an Alias from the returned base instance.
  template <typename Class>
  void construct(value_and_holder &v_h, Cpp<Class> *ptr, bool need_alias) {
      no_nullptr(ptr);
      if (Class::has_alias && need_alias && !is_alias<Class>(ptr)) {
          // We're going to try to construct an alias by moving the cpp type.  Whether or not
          // that succeeds, we still need to destroy the original cpp pointer (either the
          // moved away leftover, if the alias construction works, or the value itself if we
          // throw an error), but we can't just call `delete ptr`: it might have a special
          // deleter, or might be shared_from_this.  So we construct a holder around it as if
          // it was a normal instance, then steal the holder away into a local variable; thus
          // the holder and destruction happens when we leave the C++ scope, and the holder
          // class gets to handle the destruction however it likes.
          v_h.value_ptr() = ptr;
          v_h.set_instance_registered(true); // To prevent init_instance from registering it
          v_h.type->init_instance(v_h.inst, nullptr); // Set up the holder
          Holder<Class> temp_holder(std::move(v_h.holder<Holder<Class>>())); // Steal the holder
          v_h.type->dealloc(v_h); // Destroys the moved-out holder remains, resets value ptr to null
          v_h.set_instance_registered(false);
  
          construct_alias_from_cpp<Class>(is_alias_constructible<Class>{}, v_h, std::move(*ptr));
      } else {
          // Otherwise the type isn't inherited, so we don't need an Alias
          v_h.value_ptr() = ptr;
      }
  }
  
  // Pointer return v2: a factory that always returns an alias instance ptr.  We simply take over
  // ownership of the pointer.
  template <typename Class, enable_if_t<Class::has_alias, int> = 0>
  void construct(value_and_holder &v_h, Alias<Class> *alias_ptr, bool) {
      no_nullptr(alias_ptr);
      v_h.value_ptr() = static_cast<Cpp<Class> *>(alias_ptr);
  }
  
  // Holder return: copy its pointer, and move or copy the returned holder into the new instance's
  // holder.  This also handles types like std::shared_ptr<T> and std::unique_ptr<T> where T is a
  // derived type (through those holder's implicit conversion from derived class holder constructors).
  template <typename Class>
  void construct(value_and_holder &v_h, Holder<Class> holder, bool need_alias) {
      auto *ptr = holder_helper<Holder<Class>>::get(holder);
      // If we need an alias, check that the held pointer is actually an alias instance
      if (Class::has_alias && need_alias && !is_alias<Class>(ptr))
          throw type_error("pybind11::init(): construction failed: returned holder-wrapped instance "
                           "is not an alias instance");
  
      v_h.value_ptr() = ptr;
      v_h.type->init_instance(v_h.inst, &holder);
  }
  
  // return-by-value version 1: returning a cpp class by value.  If the class has an alias and an
  // alias is required the alias must have an `Alias(Cpp &&)` constructor so that we can construct
  // the alias from the base when needed (i.e. because of Python-side inheritance).  When we don't
  // need it, we simply move-construct the cpp value into a new instance.
  template <typename Class>
  void construct(value_and_holder &v_h, Cpp<Class> &&result, bool need_alias) {
      static_assert(std::is_move_constructible<Cpp<Class>>::value,
          "pybind11::init() return-by-value factory function requires a movable class");
      if (Class::has_alias && need_alias)
          construct_alias_from_cpp<Class>(is_alias_constructible<Class>{}, v_h, std::move(result));
      else
          v_h.value_ptr() = new Cpp<Class>(std::move(result));
  }
  
  // return-by-value version 2: returning a value of the alias type itself.  We move-construct an
  // Alias instance (even if no the python-side inheritance is involved).  The is intended for
  // cases where Alias initialization is always desired.
  template <typename Class>
  void construct(value_and_holder &v_h, Alias<Class> &&result, bool) {
      static_assert(std::is_move_constructible<Alias<Class>>::value,
          "pybind11::init() return-by-alias-value factory function requires a movable alias class");
      v_h.value_ptr() = new Alias<Class>(std::move(result));
  }
  
  // Implementing class for py::init<...>()
  template <typename... Args>
  struct constructor {
      template <typename Class, typename... Extra, enable_if_t<!Class::has_alias, int> = 0>
      static void execute(Class &cl, const Extra&... extra) {
          cl.def("__init__", [](value_and_holder &v_h, Args... args) {
              v_h.value_ptr() = construct_or_initialize<Cpp<Class>>(std::forward<Args>(args)...);
          }, is_new_style_constructor(), extra...);
      }
  
      template <typename Class, typename... Extra,
                enable_if_t<Class::has_alias &&
                            std::is_constructible<Cpp<Class>, Args...>::value, int> = 0>
      static void execute(Class &cl, const Extra&... extra) {
          cl.def("__init__", [](value_and_holder &v_h, Args... args) {
              if (Py_TYPE(v_h.inst) == v_h.type->type)
                  v_h.value_ptr() = construct_or_initialize<Cpp<Class>>(std::forward<Args>(args)...);
              else
                  v_h.value_ptr() = construct_or_initialize<Alias<Class>>(std::forward<Args>(args)...);
          }, is_new_style_constructor(), extra...);
      }
  
      template <typename Class, typename... Extra,
                enable_if_t<Class::has_alias &&
                            !std::is_constructible<Cpp<Class>, Args...>::value, int> = 0>
      static void execute(Class &cl, const Extra&... extra) {
          cl.def("__init__", [](value_and_holder &v_h, Args... args) {
              v_h.value_ptr() = construct_or_initialize<Alias<Class>>(std::forward<Args>(args)...);
          }, is_new_style_constructor(), extra...);
      }
  };
  
  // Implementing class for py::init_alias<...>()
  template <typename... Args> struct alias_constructor {
      template <typename Class, typename... Extra,
                enable_if_t<Class::has_alias && std::is_constructible<Alias<Class>, Args...>::value, int> = 0>
      static void execute(Class &cl, const Extra&... extra) {
          cl.def("__init__", [](value_and_holder &v_h, Args... args) {
              v_h.value_ptr() = construct_or_initialize<Alias<Class>>(std::forward<Args>(args)...);
          }, is_new_style_constructor(), extra...);
      }
  };
  
  // Implementation class for py::init(Func) and py::init(Func, AliasFunc)
  template <typename CFunc, typename AFunc = void_type (*)(),
            typename = function_signature_t<CFunc>, typename = function_signature_t<AFunc>>
  struct factory;
  
  // Specialization for py::init(Func)
  template <typename Func, typename Return, typename... Args>
  struct factory<Func, void_type (*)(), Return(Args...)> {
      remove_reference_t<Func> class_factory;
  
      factory(Func &&f) : class_factory(std::forward<Func>(f)) { }
  
      // The given class either has no alias or has no separate alias factory;
      // this always constructs the class itself.  If the class is registered with an alias
      // type and an alias instance is needed (i.e. because the final type is a Python class
      // inheriting from the C++ type) the returned value needs to either already be an alias
      // instance, or the alias needs to be constructible from a `Class &&` argument.
      template <typename Class, typename... Extra>
      void execute(Class &cl, const Extra &...extra) && {
          #if defined(PYBIND11_CPP14)
          cl.def("__init__", [func = std::move(class_factory)]
          #else
          auto &func = class_factory;
          cl.def("__init__", [func]
          #endif
          (value_and_holder &v_h, Args... args) {
              construct<Class>(v_h, func(std::forward<Args>(args)...),
                               Py_TYPE(v_h.inst) != v_h.type->type);
          }, is_new_style_constructor(), extra...);
      }
  };
  
  // Specialization for py::init(Func, AliasFunc)
  template <typename CFunc, typename AFunc,
            typename CReturn, typename... CArgs, typename AReturn, typename... AArgs>
  struct factory<CFunc, AFunc, CReturn(CArgs...), AReturn(AArgs...)> {
      static_assert(sizeof...(CArgs) == sizeof...(AArgs),
                    "pybind11::init(class_factory, alias_factory): class and alias factories "
                    "must have identical argument signatures");
      static_assert(all_of<std::is_same<CArgs, AArgs>...>::value,
                    "pybind11::init(class_factory, alias_factory): class and alias factories "
                    "must have identical argument signatures");
  
      remove_reference_t<CFunc> class_factory;
      remove_reference_t<AFunc> alias_factory;
  
      factory(CFunc &&c, AFunc &&a)
          : class_factory(std::forward<CFunc>(c)), alias_factory(std::forward<AFunc>(a)) { }
  
      // The class factory is called when the `self` type passed to `__init__` is the direct
      // class (i.e. not inherited), the alias factory when `self` is a Python-side subtype.
      template <typename Class, typename... Extra>
      void execute(Class &cl, const Extra&... extra) && {
          static_assert(Class::has_alias, "The two-argument version of `py::init()` can "
                                          "only be used if the class has an alias");
          #if defined(PYBIND11_CPP14)
          cl.def("__init__", [class_func = std::move(class_factory), alias_func = std::move(alias_factory)]
          #else
          auto &class_func = class_factory;
          auto &alias_func = alias_factory;
          cl.def("__init__", [class_func, alias_func]
          #endif
          (value_and_holder &v_h, CArgs... args) {
              if (Py_TYPE(v_h.inst) == v_h.type->type)
                  // If the instance type equals the registered type we don't have inheritance, so
                  // don't need the alias and can construct using the class function:
                  construct<Class>(v_h, class_func(std::forward<CArgs>(args)...), false);
              else
                  construct<Class>(v_h, alias_func(std::forward<CArgs>(args)...), true);
          }, is_new_style_constructor(), extra...);
      }
  };
  
  /// Set just the C++ state. Same as `__init__`.
  template <typename Class, typename T>
  void setstate(value_and_holder &v_h, T &&result, bool need_alias) {
      construct<Class>(v_h, std::forward<T>(result), need_alias);
  }
  
  /// Set both the C++ and Python states
  template <typename Class, typename T, typename O,
            enable_if_t<std::is_convertible<O, handle>::value, int> = 0>
  void setstate(value_and_holder &v_h, std::pair<T, O> &&result, bool need_alias) {
      construct<Class>(v_h, std::move(result.first), need_alias);
      setattr((PyObject *) v_h.inst, "__dict__", result.second);
  }
  
  /// Implementation for py::pickle(GetState, SetState)
  template <typename Get, typename Set,
            typename = function_signature_t<Get>, typename = function_signature_t<Set>>
  struct pickle_factory;
  
  template <typename Get, typename Set,
            typename RetState, typename Self, typename NewInstance, typename ArgState>
  struct pickle_factory<Get, Set, RetState(Self), NewInstance(ArgState)> {
      static_assert(std::is_same<intrinsic_t<RetState>, intrinsic_t<ArgState>>::value,
                    "The type returned by `__getstate__` must be the same "
                    "as the argument accepted by `__setstate__`");
  
      remove_reference_t<Get> get;
      remove_reference_t<Set> set;
  
      pickle_factory(Get get, Set set)
          : get(std::forward<Get>(get)), set(std::forward<Set>(set)) { }
  
      template <typename Class, typename... Extra>
      void execute(Class &cl, const Extra &...extra) && {
          cl.def("__getstate__", std::move(get));
  
  #if defined(PYBIND11_CPP14)
          cl.def("__setstate__", [func = std::move(set)]
  #else
          auto &func = set;
          cl.def("__setstate__", [func]
  #endif
          (value_and_holder &v_h, ArgState state) {
              setstate<Class>(v_h, func(std::forward<ArgState>(state)),
                              Py_TYPE(v_h.inst) != v_h.type->type);
          }, is_new_style_constructor(), extra...);
      }
  };
  
  PYBIND11_NAMESPACE_END(initimpl)
  PYBIND11_NAMESPACE_END(detail)
  PYBIND11_NAMESPACE_END(pybind11)
  