是否有可能重复在运行时MPL :: vector的无载体实例化类型？ [英] Is it possible to iterate an mpl::vector at run time without instantiating the types in the vector?

问题描述

一般情况下，我会使用的boost :: MPL :: for_each的＆LT;＆GT;（）来遍历的boost :: MPL ::矢量，但这需要使用模板功能的仿函数声明如下所示：

Generally, I would use boost::mpl::for_each<>() to traverse a boost::mpl::vector, but this requires a functor with a template function declared like the following:

模板＆LT; typename的T＆GT; void运算符（）（T＆安培;）{T :: staticCall（）;}

我这个问题是，我不希望对象T可通过的for_each＆LT被实例化;＆GT; 。我根本就不需要在运算符（） t参数。有没有办法做到这一点，或者到其他的for_each＆LT;＆GT; 不T类型的对象传递给模板函数

My problem with this is that I don't want the object T to be instantiated by for_each<>. I don't need the T parameter in the operator() at all. Is there a way to accomplish this, or an alternative to for_each<> that doesn't pass an object of type T to the template function?

理想情况下，我想运营商（）定义如下：

Optimally, I would like the operator() definition to look like this:

模板＆LT; typename的T＆GT; void运算符（）（）{T :: staticCall（）;}

当然，我不想T可在所有之前的呼叫被实例化。任何其他提示/建议也是欢迎的。

And of course, I don't want T to be instantiated at all prior to the call. Any other tips/suggestions are also welcome.

推荐答案

有趣的问题！据我所知，Boost.MPL似乎并没有提供这样的算法。然而，编写自己不应该使用迭代器是太困难了。

Interesting question! As far as I can tell, Boost.MPL does not seem to provide such an algorithm. However, writing your own should not be too difficult using iterators.

下面是一个可能的解决方案：

Here is a possible solution:

#include <boost/mpl/begin_end.hpp>
#include <boost/mpl/next_prior.hpp>
#include <boost/mpl/vector.hpp>

using namespace boost::mpl;


namespace detail {

template < typename Begin, typename End, typename F >
struct static_for_each
{
    static void call( )
    {
        typedef typename Begin::type currentType;

        F::template call< currentType >();
        static_for_each< typename next< Begin >::type, End, F >::call();
    }
};


template < typename End, typename F >
struct static_for_each< End, End, F >
{
    static void call( )
    {
    }
};

} // namespace detail


template < typename Sequence, typename F >
void static_for_each( )
{
    typedef typename begin< Sequence >::type begin;
    typedef typename end< Sequence >::type   end;

    detail::static_for_each< begin, end, F >::call();
}

[命名可能不会很好选择，但远...]

[The naming may not be very well chosen, but well...]

下面是你将如何使用这个算法：

Here is how you would use this algorithm:

struct Foo
{
    static void staticMemberFunction( )
    {
        std::cout << "Foo";
    }
};


struct Bar
{
    static void staticMemberFunction( )
    {
        std::cout << "Bar";
    }
};


struct CallStaticMemberFunction
{
    template < typename T >
    static void call()
    {
        T::staticMemberFunction();
    }
};


int main()
{
    typedef vector< Foo, Bar > sequence;

    static_for_each< sequence, CallStaticMemberFunction >(); // prints "FooBar"
}

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