[Swig-devel] [ swig-Bugs-2218834 ] Namespace breaks %ignore with unbound C++ operator<<

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Bugs item #2218834, was opened at 2008-11-03 12:03
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Category: python
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Andy Buckley (andybuckley)
Assigned to: Nobody/Anonymous (nobody)
Summary: Namespace breaks %ignore with unbound C++ operator<<

Initial Comment:
NB. This may be in the C++ parser rather than anything Python-specific, but I've only tested in Python.

I've been trying to hide a C++ operator<< function (2 args unbound, i.e. not a class method) using the SWIG %ignore directive. It seems that if this stream function is declared as a friend in the class to be streamed, inside a namespace, then the %ignore matching fails, even in the case of an exact textual match. Here's an example hepmc.i file, with the C++ code to be mapped represented inline:

-----
%module hepmc

// These don't work:
namespace HepMC {
  %ignore operator<<;
  %ignore operator<<(std::ostream&, const GenParticle&);
}
%ignore HepMC::operator<<;
%ignore HepMC::operator<<(std::ostream&, const GenParticle&);

// This works:
//%ignore operator<<;
//%ignore operator<<(std::ostream&, const GenParticle&);


/////////////////////////////////////////
// Equiv to: %include "HepMC/GenParticle.h"
namespace HepMC {
  class GenParticle {
   // [...]
   friend std::ostream& operator<<( std::ostream&, const GenParticle& );
  };

  std::ostream& operator<<( std::ostream& os, const GenParticle& gp) {
    os << gp.foo();
    return os;
  }
}
/////////////////////////////////////////
-----

The above results in an error " Warning(503): Can't wrap 'operator <<' unless renamed to a valid identifier." referring specifically to the friend statement, unless the "coarse match" %ignores under the "This works" comment are included. The equivalent %ignores which are specific, one way or another, about the namespace don't match the operator<< referred to in the friend statement.

Note that this bug seems to be specific to the friend statement --- if you remove the friend declaration in GenParticle, the %ignore works properly.


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