Constructor from initializer_list

问题

I am implementing a container in c++, a wrapper for an array in fact. I am not sure how to implement a constructor from initializer_list. I end up with this implementation but it seems to me really ugly. So could be an array allocated in a heap initialized by an initializer_list. Or is there an elegant way how to do it?

template <typename T> class sequence {
public:
    sequence (size_t n): _data {new T[n]}, _size {n} {};
    sequence (std::initializer_list<T> source);
    ~sequence() { delete[] _data; };
private:
    pointer     _data;
    size_type   _size;
};

//Initializer list constructor
template <class T> sequence<T>::sequence (std::initializer_list<T> source)
: sequence(source.size()) {
    auto iterator = source.begin();
    for ( int i=0; i < _size; i++) {
        _data[i] = *iterator;
        ++iterator;
    }
};

回答1:

Depends on what you're trying to do.

If you're actually needing to use a sequence with bounded size, as determined at compile-time, then use std::array<T,std::size_t>, which is a wrapper around a C-style array (like what you are implementing), introduced in C++11.

However, as you said in one of your comments, you're doing this mostly for educational purposes. In that case, what you have is decent. The syntax could be cleaned up a little. Consider:

//Initializer list constructor
template <class T> 
sequence<T>::sequence (std::initializer_list<T> source)
  : sequence(source.size()) 
{
  auto it = source.begin();
  auto const e = source.cend();
  auto d = data_;
  while (it != e) {
     *d++ = *it++;
  } 
};

That way you don't explicitly rely on the size(). You could consider making things more efficient by turning the it and e iterators into "move" iterators:

auto it = std::make_move_iterator(source.begin());
auto e = std::make_move_iterator(source.end());

That way, whenever it's dereferenced, its value is cast to an rvalue reference, allowing a move assignment.

来源：https://stackoverflow.com/questions/37682360/constructor-from-initializer-list

标签

c++

constructor

initializer-list