Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!brunix!sdm
From: sdm@cs.brown.edu (Scott Meyers)
Newsgroups: comp.lang.c++
Subject: g++ wrappers
Message-ID: <30179@brunix.UUCP>
Date: 22 Feb 90 05:59:07 GMT
Sender: news@brunix.UUCP
Reply-To: sdm@cs.brown.edu (Scott Meyers)
Organization: Brown University Department of Computer Science
Lines: 53

// I'm having trouble making g++ wrappers work correctly.  The only
// documentation I have to go on is the "User's Guide to GNU C++," the
// paper "Solving the RPC problem in GNU C++" from the Denver USENIX C++
// Conference, and the program twrapper.cc from the test directory of
// libg++ (1.36.3).  Unfortunately, the User's Guide and the paper seem to
// be out of date, because g++ insists that wrappers take an int as their
// first argument, and the example program offers no insight into when
// wrappers are called and when they're not.
//
// Questions:
//   -   In the program below, why doesn't the statement "object.f()" call
//       the wrapper?
//   -   In the program below, why does the statement "object.WrapperTest::f()"
//       elicit an error?

#include <stream.h>

class WrapperTest {
public:
  void f() { cout << "** In f **\n"; }

  void ()WrapperTest(int, void (WrapperTest::*pf)())
    {
      cout << "Entering wrapper...\n";
      (this->*f)();
      cout << "Exiting wrapper...\n";
    }
};
    
main()
{
  WrapperTest object;

  object.f();                 // calls f, but not the wrapper

  object.WrapperTest::()f();  // error:  no member function
                              //         `WrapperTest::wrapper for `f''
}

// More questions:
//    -   Why do wrappers have to have an int as a first argument?
//    -   What are anti-wrappers (mentioned in the source code to g++)?
//    -   Under what conditions are wrappers called, if it's no longer under
//        control of the wrapper predicate (which does not seem to be the case
//        in the above example)?
// 
// 
// All illumination appreciated,
// 
// Scott
// sdm@cs.brown.edu