class a : public B {};

class OriginalClass {
	public:
	OriginalClass() {}
	OriginalClass& fctA() { .....; return *this; }
	OriginalClass& fctD() { .....; return *this; }
};

OriginalClass inst;
isnt.fctA().fctB();

class BaseClass {
	public:
	BaseClass() {}
	BaseClass& fctA() { .....; return *this; }
};
class DerivedClass : public  BaseClass {
	public:
	DerivedClass() {}
	DerivedClass& fctD() { return *this; }
};

DerivedClass inst;
isnt.fctA().fctB();    ==> compilation error

template<class DERIVED>
class BaseClass {
	public:
	BaseClass() {}
	DERIVED& fctA() { return *static_cast<DERIVED*>(this); }
};
class DerivedClass : public  BaseClass<DerivedClass> {
	public:
	DerivedClass() {}
	DerivedClass& fctD() { return *this; }
};

DerivedClass inst;
isnt.fctA().fctB();