Re: [sigc] Unwanted pass-by-value behavior with MSVC++ 7.1

[Martin Schulze <martin-ml hippogriff de>]

Am 07.07.2004 01:17:57 schrieb(en) James Lin:
> Hi,
>
> A couple weeks ago, I posted a problem with unwanted pass-by-value
> behavior I
> ran into with libsigc++ 2.0.3 and MSVC++ 7.1. (I'm not sure if that
> message
> ever got past the moderation system.)

Hi!

I'm afraid the email you are referring to didn't reach the list.

It would be great if you submitted seperate bug reports for your issues  
at bugzilla.gnome.org. I will try to catch up with the problems at the  
weekend. Unfortunately, I don't have access to a MSVC system so I can't  
test any changes. => Patches (against current cvs) are of course  
appreciated :)

Thanks!

 Martin

> Basically sigc::bind somehow was causing arguments to be passed by
> value even
> when explicitly told to pass by reference. (I verified this by  
> passing
> an
> object by reference that had a private copy-constructor and getting a
> compile-time error.  Also, test_lambda was producing incorrect  
> results
> (unrelated to the compiler optimization problem I mentioned earlier
> today).)
>
> I'm not exactly sure why, but sun_forte_workaround appears to be the
> culprit.
> (To get libsigc++ to compile at all with the MSVC++ 7.1 compiler, I
> need to
> disable the LIBSIGC_TEMPLATE_PREFIX macro.  However, both
> LIBSIGC_TEMPLATE_PREFIX and sun_forte_workaround are controlled by  
> the
> existence of SIGC_TEMPLATE_SPECIALIZATION_OPERATOR_OVERLOAD;  
> disabling
> LIBSIGC_TEMPLATE_PREFIX means enabling sun_forte_workaround.)
>
> Anyhow, in adaptor_trait.h, changing:
>
>   #ifdef SIGC_TEMPLATE_SPECIALIZATION_OPERATOR_OVERLOAD
>     #define SIGC_WORKAROUND_OPERATOR_PARENTHESES operator()
>   #else
>     #define SIGC_WORKAROUND_OPERATOR_PARENTHESES sun_forte_workaround
>   #endif
>
> to:
>
>   #if    defined(SIGC_TEMPLATE_SPECIALIZATION_OPERATOR_OVERLOAD) \
>       || defined(WIN32)
>     #define SIGC_WORKAROUND_OPERATOR_PARENTHESES operator()
>
>   // ...
>
> seems to fix my problem.  I guess the comment in adaptor_trait.h is
> correct:
>
>   // TODO: This should have its own test, without using operator()
>   #ifdef SIGC_TEMPLATE_SPECIALIZATION_OPERATOR_OVERLOAD
>     #define LIBSIGC_TEMPLATE_PREFIX template
>   ...
>
> and that SIGC_WORKAROUND_OPERATOR_PARENTHESES and
> LIBSIGC_TEMPLATE_PREFIX
> really do need their own, independent tests.
>
> On a related note, all of the  
> SIGC_TEMPLATE_SPECIALIZATION_OPERATOR_OVERLOAD
> preprocessor conditionals test only for existence, not for value.  In
> aclocal.m4, however, there's a line:
>
>   AC_DEFINE([SIGC_TEMPLATE_SPECIALIZATION_OPERATOR_OVERLOAD],[0])
>
> I'm not familiar with m4 or with autoconf, but I assume that this
> generates a
> line:
>
>   #define SIGC_TEMPLATE_SPECIALIZATION_OPERATOR_OVERLOAD 0
>
> which would be wrong.  Shouldn't the preprocessor conditionals use  
> #if
> FOO
> instead of #ifdef FOO?
>
> - James
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