22 General utilities library [utilities]

22.5 Optional objects [optional]

using iterator       = implementation-defined;
using const_iterator = implementation-defined;

These types model contiguous_iterator ([iterator.concept.contiguous]), meet the Cpp17RandomAccessIterator requirements ([random.access.iterators]), and meet the requirements for constexpr iterators ([iterator.requirements.general]), with value type remove_cv_t<T>.

The reference type is T& for iterator and const T& for const_iterator.

All requirements on container iterators ([container.reqmts]) apply to optional::iterator and optional::const_iterator as well.

Any operation that initializes or destroys the contained value of an optional object invalidates all iterators into that object.

constexpr iterator begin() noexcept;
constexpr const_iterator begin() const noexcept;

Returns: If has_value() is true, an iterator referring to the contained value.

Otherwise, a past-the-end iterator value.

constexpr iterator end() noexcept;
constexpr const_iterator end() const noexcept;

Returns: begin() + has_value().