[英]Iterator adaptor that calls a member function when dereferenced
我試圖編寫一個迭代器適配器,每次解除引用時都應調用一個成員函數(或訪問該對象的成員)。 以下是此類API的示例:
vector<pair<int,int>> ps = {{1,"a"}, {2,"b"}, {3,"c"}};
// Pairs that represent ranges
auto rf = make_adaptor(ps.begin(), ps.end(), [](const auto& x) {return x.first;}
auto rs = make_adaptor(ps.begin(), ps.end(), [](auto& x) {return x.second;}
應打印123
:
for_each(rf.first, rf.second, [](const auto& x){std::cout << x;});
應該在ps
設置對的每個second
元素:
for_each(rs.first, rs.second, [](auto& x){ x = "hello";});
我曾嘗試使用make_adaptor
方法編寫自己的iterator
類型,但我似乎無法讓它工作:
template <typename Iterator, typename UnaryOp>
struct adaptor {
using value_type = std::result_of<UnaryOp(typename Iterator::reference)>::type;
using reference = value_type&;
using pointer = value_type*;
using difference_type = typename Iterator::difference_type;
using iterator_category = typename Iterator::iterator_category;
adaptor(){};
adaptor(Iterator it, UnaryOp func) : _it(it), _func(func) {}
reference operator*() const { return _func(*_it); }
pointer operator->() const { return &_func(*_it); }
bool operator==(const adaptor& other) const { return _it == other._it; }
bool operator!=(const adaptor& other) const { return _it != other._it; }
adaptor& operator++() {
++_it;
return *this;
}
Iterator _it;
UnaryOp _func;
};
template <typename Iterator, typename UnaryOp>
auto make_adaptor(Iterator first, Iterator last, UnaryOp func) {
return std::make_pair(adaptor<Iterator, UnaryOp>(first, func),
adaptor<Iterator, UnaryOp>(last, func));
};
原因如下:假設我有一個在points
上工作的算法convex_hull
。 但是現在我有了包含points
作為成員的對象( struct A { points pos;};
)。 我想在A
的集合上調用convex_hull
。
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