class Object
{
public:
void mem_func();
}
我希望能够在编译时从指向成员函数Object
的指针中提取类型&Object::mem_func
,但是没有注意到<type_traits>
中可以用来获取类型的任何内容。类型。
这对于具有抽象数据成员的Pimpl类是理想的,该成员随后将其转换为非抽象类,具体取决于其公共类层次结构以与std::invoke
配合使用。
编辑:,应Ilan Keshet的要求,并且由于Yakk-Adam Nevraumont提出的解决方案无法解决我拥有的额外间接层。
下面是我要做什么的更完整的想法。我想使用Qt的QAbstractSlider和QSlider类来实现范围滑块类。也许我以错误的方式来解决问题,如果是的话,请指导我采用更好的设计模式/策略来实现此目的。
// RangeSlider.h
class AbstractRangeSliderPrivate;
class AbstractRangeSlider : public QWidget
{
Q_OBJECT
Q_DECLARE_PRIVATE_D(d_ptr_, AbstractRangeSlider)
public:
explicit AbstractRangeSlider(QWidget * parent = nullptr)
: QWidget(parent)
, d_ptr_(new AbstractRangeSliderPrivate{ this, new QAbstractSlider{ this }, new QAbstractSlider{ this } })
{}
virtual ~AbstractRangeSlider() override
{}
int minimum() const
{
Q_D(const AbstractRangeSlider);
return d->getTemplate(&QAbstractSlider::minimum);
}
void setMinimum(int min) const
{
Q_D(AbstractRangeSlider);
return d->setTemplate(&QAbstractSlider::setMinimum, min);
}
int maximum() const;
void setMaximum(int max);
//... etc
protected:
AbstractRangeSlider(AbstractRangeSliderPrivate & dd, QWidget * parent)
: QWidget(parent)
: d_ptr_(&dd)
{
}
QScopedPointer<AbstractRangeSliderPrivate> const d_ptr_;
};
class RangeSliderPrivate;
class RangeSlider : public AbstractRangeSlider
{
Q_OBJECT
Q_DECLARE_PRIVATE_D(d_ptr_, RangeSlider)
public:
RangeSlider(QWidget * parent = nullptr)
: AbstractRangeSlider(new RangeSliderPrivate{ this, QSlider{ this }, QSlider{ this } }, parent)
{
}
virtual ~RangeSlider() override
{
}
// These need to be cast from QAbstractSlider in the get/setTemplates
// since these member functions are only in the derived slider class.
QSlider::TickPosition tickPosition() const
{
Q_D(RangeSlider);
return d->getTemplate(&QSlider::tickPosition);
}
void setTickPosition(QSlider::TickPosition position)
{
Q_D(RangeSlider);
return d->setTemplate(&QSlider::setTickPosition, position);
}
// etc
};
// RangeSlider_p.h
#include "AbstractRangeSlider.h"
#include <QAbstractSlider>
#include <utility>
class AbstractRangeSliderPrivate
: public MixinPrivate<AbstractRangeSliderPrivate, QAbstractSlider>
{
Q_DECLARE_PUBLIC(AbstractRangeSlider)
public:
AbstractRangeSlider * q_ptr;
AbstractRangeSliderPrivate(AbstractRangeSlider * q)
: q_ptr(q)
{}
~AbstractRangeSliderPrivate()
{}
void init(QAbstractSlider * lowSlider, QAbstractSlider * highSlider_)
{
lowSlider_ = lowSlider;
highSlider_ = highSlider;
}
template <typename Func>
auto getTemplate(Func func) const
{
// I want to cast these from AbstractRangeSlider to a concrete type such as QSlider when necessary
assert(std::invoke(func, static_cast<???>(lowSlider_))) == std::invoke(func, static_cast<???>(highSlider_)));
return std::invoke(func, static_cast<???>(lowSlider_));
}
template <typename Func, typename... Args>
void setTemplate(Func func, Args && ... args)
{
std::invoke(func, static_cast<???>(lowSlider_)), std::forward<Args>(args)...);
std::invoke(func, static_cast<???>(highSlider_)), std::forward<Args>(args)...);
}
AbstractRangeSlider * lowSlider_;
AbstractRangeSlider * highSlider_;
};
答案 0 :(得分:1)
template<auto x>
struct memfunc_object;
template<auto x>
using memfunc_object_t=typename memfunc_object<x>::type;
template<class T, class R, class...Args, R(T::*mf)(Args...)>
struct memfunc_object< mf > {
using type=T;
};
需要c++17。
没有它,您可以执行decltype(&bob::hello)
并编写类似的特征类以提取T
。
template<class M>
struct memfunc_t_object;
template<class M>
using memfunc_t_object_t=typename memfunc_t_object<M>::type;
template<class T, class R, class...Args>
struct memfunc_t_object< R(T::*)(Args...) > {
using type=T;
};