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I am trying to understand the following code. Derived is a derived structure from T and what does "," means and then Fallback {}
template <class T>
struct has_FlowTraits<T, true>
{
struct Fallback { bool flow; };
struct Derived : T, Fallback { }; //What does it means ?
template<typename C>
static char (&f(SameType<bool Fallback::*, &C::flow>*))[1];
template<typename C>
static char (&f(...))[2];
public:
static bool const value = sizeof(f<Derived>(0)) == 2;
};
767
It is possible to inherit from a template class. All the usual rules for inheritance and polymorphism apply. If we want the new, derived class to be generic it should also be a template class; and pass its template parameter along to the base class.
An individual class defines how a group of objects can be constructed, while a class template defines how a group of classes can be generated. Note the distinction between the terms class template and template class: Class template.
Templates are a feature of the C++ programming language that allows functions and classes to operate with generic types. This allows a function or class to work on many different data types without being rewritten for each one.
Explanation: Class derived template is derived from regular non-templated C++ class or templated class.
It's an implementation of Member Detector Idiom. It uses SFINAE to check whether type T has got a member called flow.
Edit: The comma part you're asking about is multiple inheritance. Struct Derived is (publicly) inheriting from both T and Fallback.
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