CPP12 — String_var and C++ implicit conversions

This e-mail addresses three CORBA C++ Revision Task Force issues:
3796
3797
4530
It also addresses section 6.10.2 of your book, "Advanced CORBA
Programming with C++" ((C) 1999).

Starting with 6.10.2 of your book, p. 164, you show an example where a
CORBA::String_var is implicitly converted to 'const char *' in a
function call, with the conversion operators as defined on p. 157 (sect.
6.10).

However, the C++ language won't choose the 'const char *() const'
operator as you (and I) would think. Instead, since the String_var
isn't const in the call's scope, the 'char *()' (i.e., non-const)
operator is chosen.

Aparently, the conversion path
String_var -> char * -> const char *
Is considered "better" than the conversion path we'd expect, namely
String_var -> const String_var -> const char *

Further, updating String_var with the resolutions of Issues 3796 and
3797 (as found in http://cgi.omg.org/issues/cxx_revision.html), namely
removing 'operator char *()' and adding 'operator char *&()' now leads
to the conversion path
String_var -> char *& -> const char *
The 'const char *' operator is still bypassed, and with 'operator char
*&()' in the picture, it seems trouble is more likely.

For reference, take a look at the USENET newsgroup comp.std.c++, the
thread of "Subject: Implicit conversion of g++", starting 2000/03/02 (I
know that long URL's don't e-mail well, but...
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm=p6qr
9dsxi04.fsf%40informatik.hu-berlin.de&rnum=1&prev=/groups%3Fhl%3Den%26lr
%3D%26ie%3DUTF-8%26oe%3DUTF-8%26selm%3Dp6qr9dsxi04.fsf%2540informatik.hu
-berlin.de)

For reference, I've attached a little source-code. Imagine that the
class is String_var. This program produces identical results under two
compilers:

• Microsoft's Visual C++ 6.0 (SP3)
• CygWin's gcc v3.2

Though the String_var implementations I've seen aren't adversely
affected, I wanted to bring this compiler behavior to your attention. I
think the CORBA & C++ folks should eventually know, too, since CORBA and
C++ seem to miss each other here.

see above