Implementation of std::initializer_list

Question

I have been looking at how the initializer_list is implemented so I found section 18.9 of the standard and found a simple enough looking interface. I thought it wou

Answer 1

This answer is not entirely accurate. It is possible to create a fully functional std::initializer_list - it just needs to meet the specific requirements of the target compiler.

For GCC and clang that requirement is a private ctor. Here is the libc++ implementation (which also happens to work fine with GCC 8.3):

template
class initializer_list
{
    const _Ep* __begin_;
    size_t    __size_;
    
    inline
    constexpr
    initializer_list(const _Ep* __b, size_t __s) noexcept
        : __begin_(__b),
          __size_(__s)
    {}
public:
    typedef _Ep        value_type;
    typedef const _Ep& reference;
    typedef const _Ep& const_reference;
    typedef size_t    size_type;
    
    typedef const _Ep* iterator;
    typedef const _Ep* const_iterator;
    
    inline
    constexpr
    initializer_list() noexcept : __begin_(nullptr), __size_(0) {}
    
    inline
    constexpr
    size_t    size()  const noexcept {return __size_;}
    
    inline
    constexpr
    const _Ep* begin() const noexcept {return __begin_;}
    
    inline
    constexpr
    const _Ep* end()   const noexcept {return __begin_ + __size_;}
};

template
inline
constexpr
const _Ep*
begin(initializer_list<_Ep> __il) noexcept
{
    return __il.begin();
}

template
inline
constexpr
const _Ep*
end(initializer_list<_Ep> __il) noexcept
{
    return __il.end();
}