finished advanced topic section of docs

example/features/old_no_macros.cpp

@@ -0,0 +1,41 @@
+
+#include <boost/contract.hpp>
+#include <cassert>
+#include <vector>
+
+//[old_no_macros
+template<typename T>
+class vector {
+public:
+    virtual void push_back(T const& value, boost::contract::virtual_* v = 0) {
+        // Program old value instead of using `OLDOF(size())` macro.
+        boost::contract::old_ptr<unsigned> old_size =
+            boost::contract::make_old(v, boost::contract::copy_old(v) ?
+                    size() : boost::contract::null_old())
+        ;
+
+        boost::contract::guard c = boost::contract::public_function(v, this)
+            .postcondition([&] {
+                BOOST_CONTRACT_ASSERT(size() == *old_size + 1);
+            })
+        ;
+
+        vect_.push_back(value);
+    }
+
+    /* ... */
+//]
+
+    unsigned size() const { return vect_.size(); }
+
+private:
+    std::vector<T> vect_;
+};
+
+int main() {
+    vector<int> vect;
+    vect.push_back(123);
+    assert(vect.size() == 1);
+    return 0;
+}
+