Optional

A library for optional (nullable) objects for C++11. This is the reference implementation of proposal N3527 (see see http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3527.html). Optional is now accepted into C++14 with modified wording as N3672. The interface is based on Fernando Cacciola's Boost.Optional library (http://www.boost.org/doc/libs/1_52_0/libs/optional/doc/html/index.html)

Supported compilers

Clang 3.2, GCC 4.6+

Usage

For usage examples and the overview see http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3527.html

Differences from N3527

• The constructor taking initializer_list argument is not constexpr. This is because initializer_list operations are not constexpr in C++11.
• In GCC versions up to, but not including, 4.8.1, member function value_or does not have rvalue reference overload. This is because rvalue overloading on *this is not supported in these versions of GCC.
• In GCC 4.6, optional<T> isn't a literal type even for trivially destructible T's. This is because of a GCC bug which causes a crash when compiling with the proposed implementation.