Listing 8

namespace original
{
    // Klasse IntStack wie in Listing 1
    class DoubleStack     
    // gleicher Aufbau wie IntStack 
    class PositiveIntStack: public IntStack
    {
        typedef IntStack Base;
        public:
            void push(const    int& i)
            {
                if (i >= 0)
                    Base::push(i);
            }
    };
    class IncrementingPositiveIntStack: public PositiveIntStack
    {
        typedef PositiveIntStack Base;
        public:
            void push(const    int& i)
            {
                if (i >= 0)
                    Base::push(i+1);
            }
    };
}
// namespace aspects wie in Listing 4
namespace composed
{
    // a simple domain specific language (DSL) 
    // for specifying aspects (implemented as
    // a bit mask)
    enum AspectDSL
    {
        none    = 0,
        tracing    = 1,
        checking= 2
    };
    // a simple generator for
    // composing aspects and classes
    template <int aspect,class Base,class Class>
    struct Compose
    {
        // parse DSL specification
        enum
        {
            subclass    = aspects::Inherits<Class,Base>::RET,
            addChecking    = aspect & checking && subclass,
            addTracing    = aspect & tracing && subclass
        };
        
        // add aspects if applicable
        typedef typename 
            aspects::IF <addChecking,aspects::Checking<Class>,Class>::RET Phase1;
        typedef typename
            aspects::IF <addTracing,aspects::Tracing<Phase1>,Phase1>::RET Phase2;
            typedef Phase2 RET; 
    };
    typedef Compose<tracing  + checking,original::IntStack,original::IntStack>::RET IntStack;
    typedef Compose<checking + tracing,original::IntStack,original::PositiveIntStack>::RET PositiveIntStack;
    typedef Compose<tracing  + checking,original::IntStack,original::IncrementingPositiveIntStack>::RET IncrementingPositiveIntStack;
    typedef Compose<tracing  + checking,original::IntStack,original::DoubleStack>::RET DoubleStack;
}