.. _program_listing_file__tmp_ws_src_proxsuite_include_proxsuite_helpers_optional.hpp:

Program Listing for File optional.hpp
=====================================

|exhale_lsh| :ref:`Return to documentation for file <file__tmp_ws_src_proxsuite_include_proxsuite_helpers_optional.hpp>` (``/tmp/ws/src/proxsuite/include/proxsuite/helpers/optional.hpp``)

.. |exhale_lsh| unicode:: U+021B0 .. UPWARDS ARROW WITH TIP LEFTWARDS

.. code-block:: cpp

   //
   // Copyright (c) 2022 INRIA
   //
   #ifndef PROXSUITE_HELPERS_OPTIONAL_HPP
   #define PROXSUITE_HELPERS_OPTIONAL_HPP
   
   #include <proxsuite/fwd.hpp>
   
   #ifdef PROXSUITE_WITH_CPP_17
   #include <optional>
   #else
   #include <proxsuite/helpers/tl-optional.hpp>
   #endif
   
   namespace proxsuite {
   #ifdef PROXSUITE_WITH_CPP_17
   template<class T>
   using optional = std::optional<T>;
   using nullopt_t = std::nullopt_t;
   inline constexpr nullopt_t nullopt = std::nullopt;
   #else
   namespace detail {
   // Source boost: https://www.boost.org/doc/libs/1_74_0/boost/none.hpp
   // the trick here is to make instance defined once as a global but in a header
   // file
   template<typename T>
   struct nullopt_instance
   {
     static const T instance;
   };
   template<typename T>
   const T nullopt_instance<T>::instance =
     T(tl::nullopt); // global, but because 'tis a template, no cpp file required
   } // namespace detail
   template<class T>
   using optional = tl::optional<T>;
   using nullopt_t = tl::nullopt_t;
   constexpr nullopt_t nullopt = detail::nullopt_instance<tl::nullopt_t>::instance;
   #endif
   } // namespace proxsuite
   
   #endif /* end of include guard PROXSUITE_HELPERS_OPTIONAL_HPP */