library_loader.h

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/*
 * This file is part of OpenTTD.
 * OpenTTD 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, version 2.
 * OpenTTD 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 OpenTTD. If not, see <http://www.gnu.org/licenses/>.
 */
 
#ifndef LIBRARY_LOADER_H
#define LIBRARY_LOADER_H
 
class LibraryLoader {
public:
  class Function {
  public:
    explicit Function(void *p) : p(p) {}
 
    template <typename T, typename = std::enable_if_t<std::is_function_v<T>>>
    operator T *() const
    {
      return reinterpret_cast<T *>(this->p);
    }
 
  private:
    void *p;
  };
 
  explicit LibraryLoader(const std::string &filename)
  {
    this->handle = this->OpenLibrary(filename);
  }
 
  ~LibraryLoader()
  {
    if (this->handle != nullptr) {
      this->CloseLibrary();
    }
  }
 
  bool HasError()
  {
    return this->error.has_value();
  }
 
  std::string GetLastError()
  {
    return this->error.value_or("No error");
  }
 
  Function GetFunction(const std::string &symbol_name)
  {
    if (this->error.has_value()) return Function(nullptr);
    return Function(this->GetSymbol(symbol_name));
  }
 
private:
  void *OpenLibrary(const std::string &filename);
 
  void CloseLibrary();
 
  void *GetSymbol(const std::string &symbol_name);
 
  std::optional<std::string> error = {}; 
  void *handle = nullptr; 
};
 
#endif /* LIBRARY_LOADER_H */