问题描述
如果以下代码符合标准，我希望得到一些反馈，并且
是否有明显的冗余或效率低下？代码的目的是
来模拟实现接口的结构FuBar的行为
InterfaceFuBar包含两个函数Fu和Bar。目标是这样做，而不是诉诸虚拟功能。
#include< iostream>
模板< typename SELF> ; struct ITABLE_InterfaceFuBar {
void（SELF :: * Fu）（）;
void（SELF :: * Bar）（）;
} ;
struct InterfaceFuBar {
struct DUMMY_InterfaceFuBar {
void Fu（）{};
void Bar（） {};
};
struct DUMMY_ITABLE_InterfaceFuBar：public
ITABLE_InterfaceFuBar< DUMMY_InterfaceFuBar> {};
DUMMY_InterfaceFuBar * mpObject;
DUMMY_ITABLE_InterfaceFuBar * mpTable;
InterfaceFuBar（void * pObject = NULL，void * pTable = NULL）{
mpObject =（DUMMY_InterfaceFuBar *）pObject;
mpTable =（DUMMY_ITABLE_InterfaceFuBar *）pTable;
};
void Fu（）{（mpObject-> *（mpTable-> Fu））（）; };
void Bar（）{（mpObject-> *（mpTable-> Bar））（）; };
};
模板< typename I，typename M> struct Implementor {
operator I（）{return I（NULL，NULL）; };
};
模板< typename M> struct Implementor< InterfaceFuBar，M> {
运算符InterfaceFuBar（）{
static ITABLE_InterfaceFuBar< M> tmp = {M :: Fu，M :: Bar};
返回InterfaceFuBar（this，（void *）& tmp）;
};
};
struct FuBar：public Implementor< InterfaceFuBar，FuBar> {
void Fu（）{std :: cout<< "福" <<的std :: ENDL; };
void Bar（）{std :: cout<< "栏" <<的std :: ENDL; };
};
int main（）{
FuBar f;
InterfaceFuBar i = f;
i.Fu（）;
std :: cin.get（）;
返回0;
}
-
Christopher Diggins
I would like some feedback if the follow code is standard compliant, and are
there any obvious redundancies or inefficiencies? The purpose of the code is
to emulate the behaviour of a struct FuBar which implements an interface
InterfaceFuBar which contains two functions Fu and Bar. The goal is to do so
without resorting to virtual functions.
#include <iostream>
template<typename SELF> struct ITABLE_InterfaceFuBar {
void(SELF::*Fu)();
void(SELF::*Bar)();
};
struct InterfaceFuBar {
struct DUMMY_InterfaceFuBar {
void Fu() { };
void Bar() { };
};
struct DUMMY_ITABLE_InterfaceFuBar : public
ITABLE_InterfaceFuBar<DUMMY_InterfaceFuBar> { };
DUMMY_InterfaceFuBar* mpObject;
DUMMY_ITABLE_InterfaceFuBar* mpTable;
InterfaceFuBar(void* pObject = NULL, void* pTable = NULL) {
mpObject = (DUMMY_InterfaceFuBar*)pObject;
mpTable = (DUMMY_ITABLE_InterfaceFuBar*)pTable;
};
void Fu() { (mpObject->*(mpTable->Fu))(); };
void Bar() { (mpObject->*(mpTable->Bar))(); };
};
template<typename I, typename M> struct Implementor {
operator I() { return I(NULL, NULL); };
};
template<typename M> struct Implementor<InterfaceFuBar, M> {
operator InterfaceFuBar() {
static ITABLE_InterfaceFuBar<M> tmp = { M::Fu, M::Bar };
return InterfaceFuBar(this, (void*)&tmp);
};
};
struct FuBar : public Implementor<InterfaceFuBar, FuBar> {
void Fu() { std::cout << "fu" << std::endl; };
void Bar() { std::cout << "bar" << std::endl; };
};
int main() {
FuBar f;
InterfaceFuBar i = f;
i.Fu();
std::cin.get();
return 0;
}
--
Christopher Diggins
http://www.cdiggins.com
http://www.heron-language.com
推荐答案
简短说明。 C风格的演员是邪恶的。改为使用C ++样式转换。
Short note. C style casts are evil. Use the C++ style casts instead.
[snip]
[snip]
你基本上是从头开始重建C ++的虚拟调度机制。这里的内容与您提供的代码
完全相同，但使用的是C ++现有的虚拟调度机制。你会发现
这个并不比上面的
代码中的手动双重间接更贵。
class InterfaceFuBar
{
struct IFB_base
{
virtual void Fu（）= 0;
虚拟空格Bar（）= 0;
};
模板< typename T>
struct IFB：public IFB_base
{
IFB（T& obj）：m_obj（obj）{}
虚拟void Fu（）
{
m_obj.Fu（）;
}
虚拟无效酒吧（）
{
m_obj.Bar（）;
}
T& m_obj;
};
IFB_base * m_pIFB;
InterfaceFuBar（）; //禁止默认初始化
InterfaceFuBar（const InterfaceFuBar&）; //禁止复制init
InterfaceFuBar& operator =（const InterfaceFuBar&）; //不允许复制
public：
template< typename T>
InterfaceFuBar（T& obj）
：m_pIFB（新IFB< T>）
{
}
~InterfaceFuBar（）
{
删除m_pIFB;
}
模板< typename T>
InterfaceFuBar& operator =（T& obj）
{
删除m_pIFB;
m_pIFB =新IFB< T> ;;
}
无福（）
{
m_pIFB-> Fu（）;
}
void Bar（）
{
m_pIFB-> Bar（）;
}
};
Claudio Puviani
PS：此代码仅供参考。我没有打扰编译或测试它，它不是例外安全等等。
You''re basically rebuilding C++''s virtual dispatch mechanism from scratch
inside InterfaceFuBar. Here''s something that does the same thing as the code
you provided, but using C++''s existing virtual dispatch mechanism. You''ll find
that this is no more expensive than the manual double indirection that''s in the
code above.
class InterfaceFuBar
{
struct IFB_base
{
virtual void Fu() = 0;
virtual void Bar() = 0;
};
template <typename T>
struct IFB : public IFB_base
{
IFB(T & obj) : m_obj(obj) {}
virtual void Fu()
{
m_obj.Fu();
}
virtual void Bar()
{
m_obj.Bar();
}
T & m_obj;
};
IFB_base * m_pIFB;
InterfaceFuBar(); // disallow default init
InterfaceFuBar(const InterfaceFuBar &); // disallow copy init
InterfaceFuBar & operator=(const InterfaceFuBar &); // disallow copy
public:
template <typename T>
InterfaceFuBar(T & obj)
: m_pIFB(new IFB<T>)
{
}
~InterfaceFuBar()
{
delete m_pIFB;
}
template <typename T>
InterfaceFuBar & operator=(T & obj)
{
delete m_pIFB;
m_pIFB = new IFB<T>;
}
void Fu()
{
m_pIFB->Fu();
}
void Bar()
{
m_pIFB->Bar();
}
};
Claudio Puviani
P.S.: This code is for illustration purposes only. I didn''t bother compiling or
testing it, it''s not exception-safe, etc.
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