SFINAE.hpp File Reference

Defines macros to enable or disable template instantiation. More...

#include <metaprogramming/TypeTraits.hpp>

Go to the source code of this file.

Macros
#define	SFINAE_ON_TEMPLATE_ARG(...)   TypeIf<(__VA_ARGS__),void*> =nullptr
#define	SFINAE_WORSEN_DEFAULT_VERSION_TEMPLATE_PARS   typename...DummyTypes /* Fake list of types */
#define	SFINAE_WORSEN_DEFAULT_VERSION_ARGS   DummyTypes... /*< Fake list of args */
	Provide empty list of args, used to unprioritize default version.
#define	SFINAE_WORSEN_DEFAULT_VERSION_ARGS_CHECK   STATIC_ASSERT_ARE_N_TYPES(0,DummyTypes)
	Check that no extra arg is passed.
#define	SFINAE_TEMPLATE_CLASS_SPECIALIZATION_PREAMBLE
#define	SFINAE_TEMPLATE_CLASS_SPECIALIZATION_ARG(TYPE)   EnableIfIs ## TYPE<TT<Ts...>,TT<Ts...>>
	To be used as an argument of the specialization.
#define	SFINAE_TEMPLATE_CLASS_SPECIALIZATION_PROVIDE_TYPE
	Provides the type inside the specialized class. More...

Detailed Description

Defines macros to enable or disable template instantiation.

http://en.cppreference.com/w/cpp/language/sfinae

Definition in file SFINAE.hpp.

Macro Definition Documentation

#define SFINAE_ON_TEMPLATE_ARG

(

...

)

TypeIf<(__VA_ARGS__),void*> =nullptr

Provides a SFINAE to be used in template par list

This follows https://stackoverflow.com/questions/32636275/sfinae-with-variadic-templates as in this example

template <typename D,
          SFINAE_ON_TEMPLATE_ARG(IsSame<D,int>)>
void foo(D i) {} // fails if D is not int

Definition at line 24 of file SFINAE.hpp.

#define SFINAE_TEMPLATE_CLASS_SPECIALIZATION_PREAMBLE

Value:

template <template<typename...> typename TT,                   \
        typename...Ts>

SFINAE for template class specialisation

Mechanism to allow the usage of SFINAE to allow a class specialization. Follows the advice of https://stackoverflow.com/a/30991097 to create a class providing the type itself

Example:

Class which needs to be explicitly specialized with SFINAE
template <typename T>
class SpecializableClass
{
};

/// Dummy type to be used to specialize the class
class SpecializingArg
{
};

PROVIDE_ENABLE_IF_FOR_TYPE(SpecializingArg);

/// Specializes the class SpecializableClass
SFINAE_TEMPLATE_CLASS_SPECIALIZATION_PREAMBLE
class SpecializableClass<SFINAE_TEMPLATE_CLASS_SPECIALIZATION_ARG(SpecializingArg)>
 {
   SFINAE_TEMPLATE_CLASS_SPECIALIZATION_PROVIDE_TYPE;

   /// To show explicit usage of T
   SpecializableClass<T>()
   {
   }
 };

Definition at line 108 of file SFINAE.hpp.

#define SFINAE_TEMPLATE_CLASS_SPECIALIZATION_PROVIDE_TYPE

Value:

       \
  using T=                                 \
      TT<Ts...>

Provides the type inside the specialized class.

Definition at line 117 of file SFINAE.hpp.

#define SFINAE_WORSEN_DEFAULT_VERSION_TEMPLATE_PARS   typename...DummyTypes /* Fake list of types */

Provides template par list to unprioritize default SFINAE

Use as last argument of a function overloaded by a other implementations using SFINAE to detect the proper version to be used. This has to be used in conjunction with the other macros SFINAE_WORSEN_DEFAULT_VERSION_ARGS and SFINAE_WORSEN_DEFAULT_VERSION_ARGS_CHECK as in this example

template <typename T,
          SFINAE_WORSEN_DEFAULT_VERSION_TEMPLATE_PARS>
int tell(T a,SFINAE_WORSEN_DEFAULT_VERSION_ARGS)
{
  SFINAE_WORSEN_DEFAULT_VERSION_ARGS_CHECK;
  return 1;
}

template <typename T,
          std::enable_if_t<sizeof(T)==4,void*> =nullptr>
decltype(auto) tell(T&& a)
{
  return a+1;
}

int main()
{
   tell(1); //returns 2

   return 0;
}

Definition at line 58 of file SFINAE.hpp.