In "Mastering the C++17 STL" book I saw both iterator and const_iterator implementation in one class using conditional for less code duplication
Here's my implementation for simple array class (most code for array class is skipped):
template<class T, size_t N>
class Array
{
public:
template<bool Const>
class ArrayIterator {
friend class Array;
public:
using difference_type = std::ptrdiff_t;
using value_type = T;
using pointer = std::conditional<Const, const value_type*, value_type*>;
using reference = std::conditional<Const, const value_type&, value_type&>;
using iterator_category = std::random_access_iterator_tag;
reference operator*() const { return *ptr; }
ArrayIterator<Const>& operator++() { ++ptr; return *this; }
ArrayIterator<Const> operator++(int) { auto res = *this; ++(*this); return res; }
template<bool R>
bool operator==(const ArrayIterator<R>& iter) const { return ptr == iter.ptr; }
template<bool R>
bool operator!=(const ArrayIterator<R>& iter) const { return ptr != iter.ptr; }
private:
explicit ArrayIterator(pointer p) : ptr(p) {};
pointer ptr;
};
using iterator = ArrayIterator<false>;
using const_iterator = ArrayIterator<true>;
iterator begin() { return iterator(data); }
iterator end() { return iterator(data + N); }
const_iterator cbegin() const { return const_iterator(data); }
const_iterator cend() const { return const_iterator(data + N); }
private:
T* data;
};
This code compiles with no errors, but iterator is kinda unusable:
Array<int, 100> arr;
/*filling it with numbers*/
int x = *arr.begin();
Gives error:
main.cpp:9:9: error: no viable conversion from 'Array<int, 100>::ArrayIterator<false>::reference' (aka 'conditional<false, const int &, int &>') to 'int'
How can I use that iterator or should I just abandon this idea from book?
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