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refs #413, #416 Implemented base_type fallthrough in Mixin::Index so it can be used by more classes.

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(cherry picked from commit d97775a232b007061cbfa85b451b0be569127696)
This commit is contained in:
Mathew Sutcliffe
2015-05-08 20:19:54 +01:00
parent 84800c190a
commit dfe42e1ce7
4 changed files with 69 additions and 17 deletions
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26
src/blackmisc/inheritance_traits.h
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@@ -45,6 +45,26 @@ namespace BlackMisc
typedef typename std::conditional<QMetaTypeId<typename BaseOf<T>::type>::Defined, typename BaseOf<T>::type, void>::type type;
};
/*!
* If T has a member typedef base_type which has a member propertyByIndex, this trait will obtain it, otherwise void.
*/
template <class T>
class IndexBaseOf
{
// http://en.wikibooks.org/wiki/More_C++_Idioms/Member_Detector
struct Empty {};
struct Fallback { int propertyByIndex; };
template <int Fallback:: *> struct int_t { typedef int type; };
template <typename U> struct Derived : public Fallback, public std::conditional<std::is_void<U>::value, Empty, U>::type {};
template <typename U> static void test(typename int_t<&Derived<U>::propertyByIndex>::type);
template <typename U> static U test(...);
public:
//! Type of T::base_type, or void if not declared.
typedef decltype(test<typename BaseOf<T>::type>(0)) type;
};
/*!
* Alias for typename BaseOf<T>::type.
*/
@@ -56,6 +76,12 @@ namespace BlackMisc
*/
template <class T>
using MetaBaseOfT = typename MetaBaseOf<T>::type;
/*!
* Alias for typename IndexBaseOf<T>::type.
*/
template <class T>
using IndexBaseOfT = typename IndexBaseOf<T>::type;
}
#endif