BLI_function_ref.hh

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/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */
 
#pragma once
 
#include <optional>
#include <type_traits>
#include <utility>
 
#include "BLI_utildefines.h"
 
#include "BLI_memory_utils.hh"
 
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;
 
  FunctionRef(std::nullptr_t) {}
 
  template<typename Callable,
           BLI_ENABLE_IF((
               !std::is_same_v<std::remove_cv_t<std::remove_reference_t<Callable>>, FunctionRef>)),
           BLI_ENABLE_IF((std::is_invocable_r_v<Ret, Callable, Params...>))>
  FunctionRef(Callable &&callable)
      : callback_(callback_fn<typename std::remove_reference_t<Callable>>),
        callable_(intptr_t(&callable))
  {
  }
 
  Ret operator()(Params... params) const
  {
    BLI_assert(callback_ != nullptr);
    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