我有一个简单的容器:
template <class T, class Allocator = std::allocator<T>>
class ring
{
public:
using value_type = T;
using allocator_type = Allocator;
using size_type = std::size_t;
using difference_type = std::ptrdiff_t;
using reference = T &;
using const_reference = const T &;
using pointer = T *;
using const_pointer = const T *;
private:
template <class E>
class ring_iterator
{
public:
using iterator_category = std::random_access_iterator_tag;
using value_type = E;
using difference_type = std::ptrdiff_t;
using reference = E &;
using pointer = E *;
ring_iterator(const ring_iterator& other) = default;
ring_iterator(ring_iterator&& other) = default;
ring_iterator& operator = (const ring_iterator& other);
pointer operator-> () const;
reference operator* () const;
ring_iterator& operator++ ();
ring_iterator operator++ (int);
ring_iterator& operator-- ();
ring_iterator operator-- (int);
ring_iterator& operator += (difference_type diff);
ring_iterator& operator -= (difference_type diff);
ring_iterator operator + (difference_type diff) const;
ring_iterator operator - (difference_type diff) const;
difference_type operator - (const ring_iterator& other) const;
bool operator == (const ring_iterator& other) const;
bool operator != (const ring_iterator& other) const;
bool operator < (const ring_iterator& other) const;
operator ring_iterator<const E>() const;
};
public:
using iterator = ring_iterator<T>;
using const_iterator = ring_iterator<const T>;
using reverse_iterator = std::reverse_iterator<iterator>;
using const_reverse_iterator = std::reverse_iterator<const_iterator>;
ring(Allocator alloc = {});
ring(size_type cap, Allocator alloc = {});
ring(const ring& other);
ring(ring&& other);
ring& operator = (const ring& other);
ring& operator = (ring&& other);
~ring();
reference front();
reference back();
const_reference front() const;
const_reference back() const;
void push_front(const value_type& val);
void push_front(value_type&& val);
void push_back(const value_type& val);
void push_back(value_type&& val);
void pop_front();
void pop_back();
void reserve(size_t);
void clear();
size_type size() const;
size_type capacity() const;
bool empty() const;
bool full() const;
reference operator[](size_type index);
const_reference operator[](size_type index) const;
reference at(size_type index);
const_reference at(size_type index) const;
iterator begin();
const_iterator begin() const;
const_iterator cbegin() const;
iterator end();
const_iterator end() const;
const_iterator cend() const;
reverse_iterator rbegin();
const_reverse_iterator rbegin() const;
const_reverse_iterator crbegin() const;
reverse_iterator rend();
const_reverse_iterator rend() const;
const_reverse_iterator crend() const;
};
我应该怎么做才能编译下面的代码?#include <vector>
#include <ranges>
//std::vector<int> v; //compiles
ring<int> v; //does not compile
auto range = v | std::views::transform([](int n) { return n * n; });
MSVC 编译器错误:error C2678: binary '|': no operator found which takes a left-hand operand of type 'ring<int,std::allocator<int>>' (or there is no acceptable conversion)
最佳答案
所以......经过大量调查:
您的迭代器必须具有公共(public)默认构造函数。
What should I do to make my container work with ranges?
它应该满足概念
std::ranges::range
:static_assert(std::ranges::range<ring<int>>);
但它没有,错误消息也没有帮助。所以我们看一下概念本身:template< class T > concept range = requires(T& t) { ranges::begin(t); // equality-preserving for forward iterators ranges::end (t); };
ranges::begin(v)
定义明确,但 ranges::end(v)
给出错误“错误:不匹配调用 '(const std::ranges::__cust_access::_End) (ring&)'”,同样,没有有用的错误消息。所以现在我们查看
std::ranges::end
:template< class T >
requires /* see below */
constexpr std::sentinel_for<ranges::iterator_t<T>> auto end(T&& t);
这里的文档有点不确定,但这里失败的要求是:static_assert(
std::sentinel_for<ring<int>::iterator, ring<int>::iterator>
);
即结束迭代器应该是开始迭代器的哨兵。在这里,我们到达了第一个有用的错误消息:
error: static assertion failed
89 | std::sentinel_for<ring<int>::iterator, ring<int>::iterator> | ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
note: constraints not satisfied
[...]
opt/compiler-explorer/gcc-trunk-20210906/include/c++/12.0.0/concepts:137:30: note: the expression
is_constructible_v<_Tp, _Args ...> [with _Tp = ring<int, std::allocator<int> >::ring_iterator<int>; _Args = {}]
evaluated to 'false'137 | = destructible<_Tp> && is_constructible_v<_Tp, _Args...>; | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
所以你有它
ring<int>::ring_iterator<int>
必须有一个公开可用的默认构造函数。
关于c++ - 我应该怎么做才能使我的容器使用范围?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/69070233/