PureAbstract

 for( auto& element : elements )
 {
   if( auto c = std::dynamic_pointer_cast<C>( element ) )
    {
       c->BehaveLikeC();
    }
 
    if( auto d = std::dynamic_pointer_cast<D>( element ) )
    {
        DoSomething(d);

PureAbstract

#include <type_traits>
#include <limits>
#include <cstdint>

namespace detail {

    template<std::uintmax_t Value>
    constexpr std::uintmax_t parse_unsigned_literal()
    {
        return Value;

PureAbstract

// ==================== 1) Overload Catch::toString
struct ts_overload { }; // have an overload of toString

namespace Catch {
    std::string toString( const ts_overload& )
    {
        return "ts:ts_overload";
    }
}