Boost.Null

• 大昔にボツになったと思われるものがSandboxにある
• しかしまた消えていた

[]#include[][] <boost/config.hpp>[]
[]namespace[] []poost[] {
[]#if[][] !defined(BOOST_NO_MEMBER_TEMPLATES)[]
  []namespace[] []detail[] {
    []struct[] []null_type[]

    {

      []// Will disable some warnings about a class with all ctors[]

      []// private and no firends[]

      []friend[] []class[] []poost_null_dummy_class[];
      []template[]< []class[] []AnyT[] >

      []operator[] []AnyT[]* () []const[] { []return[] 0; }
      []template[]< []class[] []AnyT[], []class[] []MemT[] >

      []operator[] []MemT[] []AnyT[]::* () []const[] { []return[] 0; }
    []private[]:

      []null_type[]();

      []null_type[]([]null_type[] []const[]&);

      []void[] []operator[]=([]null_type[] []const[]&);

      []void[] []operator[]&() []const[];

    };
  } []// namespace detail[]
[]namespace[] {
[]// Workaround: static is still required for broken stdafx.cpp[]

[]// Null reference ? Can't call null_type::null_type(), so ...[]

[]static[] []detail[]::[]null_type[] []const[]& []null[] = *([]detail[]::[]null_type[]*)0;
} []// namespace poost::anonymous[]
[]#else[]
[]namespace[] {
[]static[] []int[] []const[] []null[] = 0;
} []// namespace poost::anonymous[]
[]#endif[][] [][]// !defined(BOOST_NO_MEMBER_TEMPLATES)[]
} []// namespace poost[]