VisitorBase Cyclic Implementation - GerdHirsch/Cpp-VisitorFrameworkCyclicAcyclic GitHub Wiki
The Repository generates the application specific visitor base
with the parameters, the repository is created: using Visitor = .
template<class LoggingPolicy, class BaseKind_, class ...Visitables>
struct Repository{
using Visitor =
typename Cyclic::SwitchBaseKind<LoggingPolicy, BaseKind_>::template
implementsVisitor<Visitables...>;
...
};
Cyclic::SwitchBaseKind is the switch between abstract and default implementations
for visit(..) which are generated via the inner template implementsVisitor<Visitables...>.
The inner template delegates to a template in namespace Cyclic InheritFrom....
namespace Cyclic{
template<class LoggingPolicy_, class = BaseKind::Abstract>
struct SwitchBaseKind{
template<class ...Visitables>
using implementsVisitor = Cyclic::InheritFromAbstract<Visitables...>;
};
template<class LoggingPolicy_>
struct SwitchBaseKind<LoggingPolicy_, BaseKind::Default>{
template<class ...Visitables>
using implementsVisitor = Cyclic::InheritFromDefault<LoggingPolicy_, Visitables...>;
};
InheritFromDefault is similar implemented like InheritFromAbstract. It is explicit specialized for one
Argument and the primary inherits from itself by reducing the list of Visitables by one type. The list is represented by
template<class ToVisit, class... Rest>. The specialization ends the recursion. This creates a structure of linear inherited baseclasses each declaring the matching signature for virtual void visit(ToVisit&) = 0; Because of name hiding, the using base_type::visit statement is needed.
template<class ToVisit, class... Rest>
struct InheritFromAbstract
: public InheritFromAbstract<Rest...>{
public:
virtual void visit(ToVisit& v) = 0;
using base_type = InheritFromAbstract<Rest...>;
using base_type::visit;
};
template<class ToVisit>
struct InheritFromAbstract<ToVisit>
{
public:
virtual void visit(ToVisit& v) = 0;
virtual std::string toString() const = 0;
};
}