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#pragma once
struct InputIteratorTag {};
struct OutputIteratorTag {};
struct ForwardIteratorTag : public InputIteratorTag {};
struct BidirectionalIteratorTag : public ForwardIteratorTag {};
struct RandomAccessIteratorTag : public BidirectionalIteratorTag {};
template
struct InputIterator
{
//typedef T ValueType;
//typedef Distance DifferenceType;
//typedef T* Pointer;
//typedef T& Reference;
typedef InputIteratorTag IteratorCategory; //迭代器的类型 （ 包括上面那5个struct ）
};
template
struct IteratorTraits
{
//typedef typename Iterator::ValueType ValueType;
//typedef typename Iterator::DifferenceType DifferenceType;
//typedef typename Iterator::Pointer Pointer;
//typedef typename Iterator::Reference Reference;
typedef typename InputIterator::IteratorCategory IteratorCategory;
};
template
struct IteratorTraits //内置类型的特化版本
{
typedef RandomAccessIteratorTag IteratorCategory;
};
template
inline size_t Distance(InputIterator first, InputIterator last)
{
return _Distance(first, last, IteratorTraits::IteratorCategory() ); //这里第三个参数 并没有实际意义，不过正是它的存在，让_Distance实现重载
}
template
inline size_t _Distance(InputIterator first, InputIterator last, RandomAccessIteratorTag)
{
return last - first;
}
template
inline size_t _Distance(InputIterator first, InputIterator last, InputIteratorTag)
{
size_t n = 0;
while (first != last)
{
++first;
++n;
}
return n;
}