Question

所以我有SkipList.hpp，它有一个名为SkipListIterator的嵌套模板类。

//SkipList.hpp
template <class Key_t, class Mapped_t>
class SkipList {
    template <bool isConst, bool isReverse>
    class SkipListIterator {
        ...
    }
    ...
}

在我的Map.hpp中，我想为不同类型的迭代器创建typedef。我试图做的是以下内容：

//Map.hpp

#include "SkipList.hpp"
template <class Key_t, class Mapped_t>
class Map {
    typedef typename SkipList<Key_t, Mapped_t>::SkipListIterator<false, false> iterator;
    typedef typename SkipList<Key_t, Mapped_t>::SkipListIterator<true, false> const_iterator;
    typedef typename SkipList<Key_t, Mapped_t>::SkipListIterator<false, true> reverse_iterator;
    typedef typename SkipList<Key_t, Mapped_t>::SkipListIterator<true, true> const_reverse_iterator;
    ...
}

这不起作用，g ++给了我以下错误：

error: non-template 'SkipListIterator' used as template
typedef typename SkipList<Key_t, Mapped_t>::SkipListIterator<false, false> iterator
                                            ^

Answer 1

这适用于gcc 6.3.1：

template <class Key_t, class Mapped_t>
class SkipList {
    template <bool isConst, bool isReverse>
    class SkipListIterator {
    };
};

template <class Key_t, class Mapped_t>
class Map {
    typedef typename SkipList<Key_t, Mapped_t>::template SkipListIterator<false, false> iterator;
    typedef typename SkipList<Key_t, Mapped_t>::template SkipListIterator<true, false> const_iterator;
    typedef typename SkipList<Key_t, Mapped_t>::template SkipListIterator<false, true> reverse_iterator;
    typedef typename SkipList<Key_t, Mapped_t>::template SkipListIterator<true, true> const_reverse_iterator;
};

使用模板时，编译器通常需要额外的帮助来确定它的类型，模板或非类型。

在模板化类中使用模板化嵌套类的Typedef

1 个答案: