BLI_function_ref.hh

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/*
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */
 
#pragma once
 
#include <optional>
#include <type_traits>
#include <utility>
 
#include "BLI_utildefines.h"
 
namespace blender {
 
template<typename Function> class FunctionRef;
 
template<typename Ret, typename... Params> class FunctionRef<Ret(Params...)> {
 private:
  Ret (*callback_)(intptr_t callable, Params... params) = nullptr;
 
  intptr_t callable_;
 
  template<typename Callable> static Ret callback_fn(intptr_t callable, Params... params)
  {
    return (*reinterpret_cast<Callable *>(callable))(std::forward<Params>(params)...);
  }
 
 public:
  FunctionRef() = default;
 
  template<typename Callable,
           std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Callable>>,
                                            FunctionRef>> * = nullptr>
  FunctionRef(Callable &&callable)
      : callback_(callback_fn<typename std::remove_reference_t<Callable>>),
        callable_(reinterpret_cast<intptr_t>(&callable))
  {
  }
 
  Ret operator()(Params... params) const
  {
    BLI_assert(callback_ != nullptr);
    return callback_(callable_, std::forward<Params>(params)...);
  }
 
  using OptionalReturnValue = std::conditional_t<std::is_void_v<Ret>, void, std::optional<Ret>>;
 
  OptionalReturnValue call_safe(Params... params) const
  {
    if constexpr (std::is_void_v<Ret>) {
      if (callback_ == nullptr) {
        return;
      }
      callback_(callable_, std::forward<Params>(params)...);
    }
    else {
      if (callback_ == nullptr) {
        return {};
      }
      return callback_(callable_, std::forward<Params>(params)...);
    }
  }
 
  operator bool() const
  {
    /* Just checking `callback_` is enough to determine if the `FunctionRef` is in a state that it
     * can be called in. */
    return callback_ != nullptr;
  }
};
 
}  // namespace blender