[boost] [python] const-correctness and get_signature

Subject: [boost] [python] const-correctness and get_signature
From: Jim Bosch (talljimbo_at_[hidden])
Date: 2010-01-16 00:30:23

I've been working on an idea to provide optional const-handling in
boost.python wrapped classes.  It's coming along pretty well, but I've
run into one major sticking point: the get_signature functions that
extract the argument types of member function pointers into mpl
sequences remove any cv-qualification on the hidden 'this' argument.
This seems to be intentional - from the comments in
python/signature.hpp:

//  Note that cv-qualification is dropped from
//  the "hidden this" argument of member functions; that is a
//  necessary sacrifice to ensure that an lvalue from_python converter
//  is used.  

This doesn't actually seem necessary; for a normal wrapped class, the
special-case lvalue converter will always be the highest priority, and
for a const member function, supporting rvalue converters as a fall-back
wouldn't do any harm that I can see (and would help me out
considerably).  Could this be a relic from before wrapped class lvalue
conversions were handled as a special case?

Anyhow, if my hypothesis is correct, and there isn't a need to drop the
cv-qualifiers in get_signature, I'd like to make a ticket and submit a
patch to change it - but I wanted to check here first to see if maybe
that breaks something else.

Thanks!

Jim Bosch