boost/boost/variant/detail/forced_return.hpp

   1 //-----------------------------------------------------------------------------
   2 // boost variant/detail/forced_return.hpp header file
   3 // See http://www.boost.org for updates, documentation, and revision history.
   4 //-----------------------------------------------------------------------------
   5 //
   6 // Copyright (c) 2003
   7 // Eric Friedman
   8 //
   9 // Distributed under the Boost Software License, Version 1.0. (See
  10 // accompanying file LICENSE_1_0.txt or copy at
  11 // http://www.boost.org/LICENSE_1_0.txt)
  12
  13 #ifndef BOOST_VARIANT_DETAIL_FORCED_RETURN_HPP
  14 #define BOOST_VARIANT_DETAIL_FORCED_RETURN_HPP
  15
  16 #include "boost/config.hpp"
  17 #include "boost/variant/detail/generic_result_type.hpp"
  18 #include "boost/assert.hpp"
  19
  20 #if !defined(BOOST_MSVC) && !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
  21 #   include "boost/type_traits/remove_reference.hpp"
  22 #endif
  23
  24 namespace boost {
  25 namespace detail { namespace variant {
  26
  27 ///////////////////////////////////////////////////////////////////////////////
  28 // (detail) function template forced_return
  29 //
  30 // Logical error to permit invocation at runtime, but (artificially) satisfies
  31 // compile-time requirement of returning a result value.
  32 //
  33
  34 #if !defined(BOOST_MSVC)                                \
  35  && !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)  \
  36  && !defined(BOOST_NO_VOID_RETURNS)
  37
  38 // "standard" implementation:
  39
  40 template <typename T>
  41 inline T forced_return( BOOST_EXPLICIT_TEMPLATE_TYPE(T) )
  42 {
  43     // logical error: should never be here! (see above)
  44     BOOST_ASSERT(false);
  45
  46     typedef typename boost::remove_reference<T>::type basic_type;
  47     basic_type* dummy = 0;
  48     return *static_cast< basic_type* >(dummy);
  49 }
  50
  51 template <>
  52 inline void forced_return<void>( BOOST_EXPLICIT_TEMPLATE_TYPE_SPEC(void) )
  53 {
  54     // logical error: should never be here! (see above)
  55     BOOST_ASSERT(false);
  56 }
  57
  58 #elif !defined(BOOST_MSVC)
  59
  60 // workaround implementation
  61 //
  62 // TODO: Determine the most efficient way to handle this -- as below? by
  63 // throwing? by recursive call to forced_return itself? etc.
  64 //
  65
  66 template <typename T>
  67 inline
  68     BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(T)
  69 forced_return( BOOST_EXPLICIT_TEMPLATE_TYPE(T) )
  70 {
  71     // logical error: should never be here! (see above)
  72     BOOST_ASSERT(false);
  73
  74     BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(T) (*dummy)() = 0;
  75     return dummy();
  76 }
  77
  78 #else // defined(BOOST_MSVC)
  79
  80 // msvc-specific implementation
  81 //
  82 // Leverages __declspec(noreturn) for optimized implementation.
  83 //
  84
  85 __declspec(noreturn)
  86 inline void forced_return_no_return() {};
  87
  88 template <typename T>
  89 inline
  90     BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(T)
  91 forced_return( BOOST_EXPLICIT_TEMPLATE_TYPE(T) )
  92 {
  93     // logical error: should never be here! (see above)
  94     BOOST_ASSERT(false);
  95
  96     forced_return_no_return();
  97 }
  98
  99 #endif // BOOST_MSVC optimization
 100
 101 }} // namespace detail::variant
 102 } // namespace boost
 103
 104 #endif // BOOST_VARIANT_DETAIL_FORCED_RETURN_HPP