Is there a way to compile-time assert if a variable is a class, struct or a basic type in c++?
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06-07-2019 - |
Question
I am trying to implement a template class that would be able to tell me if a variable is a class,structure or a basic type.
So far I've come with this:
template< typename T >
class is_class
{
private:
template< typename X >
static char ( &i_class( void(X::*)() ) )[1];
//
template< typename X >
static char ( &i_class( X ) )[2];
public:
static bool const val = sizeof( i_class< T >(0) ) == 1;
};
and ussage:
is_class< int >::val; // false
is_class< some_class_type >::val; // true
The problem is that now I need to write a blank void function in every class that could be used with this code.
Does anyone know a solution to this problem?
Solution
is_class
is a member of the Boost.Type_Traits library. The implementation is probably similar to what you already have. You would use in in conjunction with enable_if
to create the function if appropriate:
template <class T>
typename enable_if_c<boost::is_class<T>::value>::type
foo() { }
Or the equivalent:
template <class T>
typename enable_if<boost::is_class<T>>::type
foo() { }
The function foo
is only generated if the type T
is of class type.
The return value for the function, if it is generated, is the second parameter (omitted) to the enable_if
template (the default is void
).
OTHER TIPS
Use boost's type traits.
If it's only asserting during compile time, you could use BOOST_STATIC_ASSERT
and Boost.TypeTraits to check if types are suitable. If you want to enable a template for specific types, you may have success using Boost's enable_if.