initial code

inheritance_functor.cpp

@@ -0,0 +1,91 @@
+#include <iostream>
+#include <vector>
+#include <iterator>
+
+#define ITEMS(c) c.begin(),c.end()
+
+template<class T>
+class Increment
+{
+    public:
+    T arg;
+    Increment( T a ) : arg(a) {}
+
+    template<typename OutIt>
+    T operator() ( T& value, OutIt out )
+    {
+        value+=arg;
+        *out++ = value;
+        return 1;
+    }
+};
+
+template<class OP, typename OutIt>
+class Functor
+{
+    public:
+    OP & op;
+    Functor( OP & o ) : op(o) {}
+
+    // we cannot put the OutIt template here, because the functor is virtual
+    virtual int operator() ( int& v, OutIt out ) = 0;
+};
+
+
+/* It is painfull to declare a Functor's derivate class with all the templates
+ * because C++ can't infer templates from parameters of the constructor.
+ * Thus, we rely on this helper free function, where templates can be infered.
+ *
+ * Instead of having to write:
+ *      Assign<Increment<int>, std::back_insert_iterator<std::vector<int> > > f(add_one);
+ * We can just write:
+ *      auto f = make_Functor<Assign>( add_one, std::back_inserter(v));
+ */
+template<
+    template< class, typename > class FC,
+    class OP,
+    typename OutIt
+>
+FC<OP,OutIt>& make_Functor( OP & op, OutIt /*out*/ )
+{
+    return *(new FC<OP,OutIt>(op));
+}
+
+
+template<class OP, typename OutIt>
+class Assign : public Functor<OP, OutIt>
+{
+    public:
+    Assign( OP & o ) : Functor<OP, OutIt>(o) {}
+
+    int operator() ( int& value, OutIt out )
+    {
+        // std::clog << value << " + " << this->op.arg << std::endl;
+        return this->op(value,out);
+    }
+};
+
+int main(void)
+{
+    size_t nb = 10000;
+
+    for( unsigned int k=0; k<nb; ++k) {
+        std::vector<int> v;
+        auto out = std::back_inserter(v);
+
+        Increment<int> add_one(1);
+
+        // we specify the output iterator here, just for type inference
+        auto f = make_Functor<Assign>(add_one, out);
+
+        int i = -1;
+        size_t n = 0;
+        for( unsigned int j=0; j<nb; ++j ) {
+            n += f(i, out);
+        }
+
+        // std::cout << v.size() << std::endl;
+        // std::copy( ITEMS(v), std::ostream_iterator<int>( std::cout, "\n") );
+    }
+}
+