用于函数对和模板特化的RAII包装器

Question

我为C函数对编写了一个RAII包装器,用于初始化和释放资源,在大多数情况下它都很适合我.

#include <GL/glfw.h>
#include <string>
#include <functional>
#include <stdexcept>

template <typename UninitFuncType,
          typename SuccessValueType,
          SuccessValueType successValue>
class RAIIWrapper
{
public:
    template <typename InitFuncType, typename... Args>
    RAIIWrapper(InitFuncType initializer,
                UninitFuncType uninitializer,
                const std::string &errorString,
                const Args&... args) : 
        uninit_func(uninitializer)
    {
        if (successValue != initializer(args...))
            throw std::runtime_error(errorString);
        initialized = true;
    }

    bool isInitialized() const
    {
        return initalized;
    }

    ~RAIIWrapper()
    {
        if (initalized)
            uninit_func();
    }

    // non-copyable
    RAIIWrapper(const RAIIWrapper &) = delete;
    RAIIWrapper& operator=(const RAIIWrapper &) = delete;

private:
    bool initalized = false;
    std::function<UninitFuncType> uninit_func;
};

using GLFWSystem = RAIIWrapper<decltype(glfwTerminate), decltype(GL_TRUE), GL_TRUE>;
using GLFWWindow = RAIIWrapper<decltype(glfwCloseWindow), decltype(GL_TRUE), GL_TRUE>;

int main()
{
    GLFWSystem glfw(glfwInit,
                    glfwTerminate,
                    "Failed to initialize GLFW");
}

但是,当一个函数返回时,void比如说Enter/LeaveCriticalSection我不确定如何在这个类中执行它.我应该把这个班专门化为SuccessValueType = void案例吗？或者使用默认模板参数应该做什么？

Answer 1

我想注意一下

1. 您不需要在包装器类中有关初始化函数的信息.您只需要了解未初始化功能.

2. 您可以创建函数帮助程序来实例化您的包装器.

我提出了以下解决方案(我喜欢@ipc异常处理的想法)

template <typename UninitF>
struct RAII_wrapper_type
{
    RAII_wrapper_type(UninitF f)
    :_f(f), _empty(false)
    {}
    RAII_wrapper_type(RAII_wrapper_type&& r)
    :_f(r._f), _empty(false)
    {
      r._empty = true;
    }

    RAII_wrapper_type(const RAII_wrapper_type&) = delete;
    void operator=(const RAII_wrapper_type&) = delete;

    ~RAII_wrapper_type()
    {
      if (!_empty) {
        _f();
      }
    }

  private:
    UninitF _f;
    bool _empty; // _empty gets true when _f is `moved out` from the object.
};

template <typename InitF, typename UninitF, typename RType, typename... Args>
RAII_wrapper_type<UninitF> capture(InitF init_f, UninitF uninit_f, RType succ, 
                                   const char* error, Args... args)
{
  if(init_f(args...) != succ) {
    throw std::runtime_error(error);
  }
  return RAII_wrapper_type<UninitF>(uninit_f);
}

template<typename InitF, typename UninitF, typename... Args>
RAII_wrapper_type<UninitF> capture(InitF init_f, UninitF uninit_f, Args... args)
{
  init_f(args...);
  return RAII_wrapper_type<UninitF>(uninit_f);
}

例:

void t_void_init(int){}
int t_int_init(){ return 1; }
void t_uninit(){}

int main()
{
  auto t1 = capture(t_void_init, t_uninit, 7);
  auto t2 = capture(t_int_init, t_uninit, 0, "some error");
}

编辑

RAII_wrapper_type应该有移动语义,我们应该小心地实现它的移动构造函数,以防止uninit_f多次调用.