Re: [boost] boost::mpl::for_each and value_initialized

Subject: Re: [boost] boost::mpl::for_each and value_initialized
From: Niels Dekker - address until 2010-10-10 (niels_address_until_2010-10-10_at_[hidden])
Date: 2010-01-22 05:06:40

>> Do I understand correctly that you want the memset call to be skipped
>> for those compiler versions that have implemented
>> value-initialization entirely correctly? Do you know exactly which
>> compiler versions do implement value-initialization correctly?

Aleksey Gurtovoy wrote:
> [...] I think we should revert to the approach of applying the workaround
> conditionally for the specific compilers known to be buggy, and just
> those -- especially if we have tests to discover these bugs should they
> return.
>
> As for the specific compiler versions:
>
> - GCC bugs #30111 and #33916 has been fixed in 4.4 and 4.2.4
>   correspondingly [1], [2].

So GCC 4.2.4 still needs the memset, but GCC >= 4.4.0 can do without it, 
right?

> - MSVC bug #100744, despite being marked as "Closed, Won't Fix" [3],
>   has actually been fixed in VC9 [4].

I'm sorry, MSVC bug #100744 is still there, even though #335987 has been 
fixed. VC9 deals with POD types correctly, but may not do so for non-POD 
aggregate class types.

> - Borland bug #51854 is also reported as being fixed in build
>   "12.0.3140.16150" [5]

Looks promising. Do you know how to do a compile-time check if 
Borland/Codegear build >= 12.0.3140.16150?

Anyway, I wouldn't mind if the memset call in utility/value_init.hpp would 
become conditional, for example as follows:

  #ifdef BOOST_VALUE_INITIALIZATION_NEEDS_MEMSET
      std::memset(&x, 0, sizeof(x));

  #endif

What do you think? And would it be okay to you to have such a macro, 
BOOST_VALUE_INITIALIZATION_NEEDS_MEMSET, defined in boost/config/compiler/, 
for those specific compiler versions?

> [1] http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30111#c10
> [2] http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916#c12
> [3]
> https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=100744
> [4]
> https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=335987
> [5] http://qc.embarcadero.com/wc/qcmain.aspx?rc=51854

Thanks!

  Kind regards, Niels

--
Niels Dekker
http://www.xs4all.nl/~nd/dekkerware
Scientific programmer at LKEB, Leiden University Medical Center