David Abrahams wrote:
https://boost-consulting.com/trac/projects/boost/build/trunk reveals that https://boost-consulting.com/trac/projects/boost/changeset/41919 introduced a failing test of the utility library.
Thanks for reminding me, Dave. The test failure actually indicates that the MSVC-workaround of value_initialized that I committed a while ago to the trunk has a bug: when a value_initialized<T> object is copied, the wrapped T object isn't copied properly. If T has an accessible copy constructor, it should be called when copy-constructing a value_initialized<T>. And if T has an accessible copy assignment operator, it should be called when assigning a value_initialized<T>. I have just committed a fix for this bug to the trunk: http://svn.boost.org/trac/boost/changeset/41942 Luckily the bug wasn't yet released! I mean, it isn't yet in Boost release version 1.34.1, and I hope we can take it out of the release branch. The commit (changeset [41942]) aims to fix some other issues as well. Fernando Cacciola (the owner of value_init) and I also decided to no longer distinguish between a "workaround version" and a non-workaround version of value_initialized<T>. Until now the workaround was only for MSVC. But it has appeared that various other compilers have value-initialization related issues: GCC Bug 30111 - Value-initialization of POD base class doesn't initialize members http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30111 GCC Bug 33916 - Default constructor fails to initialize array members http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916 Borland Report 51854 - Value-initialization: POD struct should be zero-initialized http://qc.codegear.com/wc/qcmain.aspx?d=51854 I recently added tests on these issues to value_init_test, and they caused a test failures on a majority of the test platforms, at http://beta.boost.org/development/tests/trunk/developer/utility_.html In general, those compilers that don't support value-initialization well forget to zero-initialize the POD-members of a type T, in some cases... The workaround is basically as follows: The constructor of value_initialized<T> stores the bytes of an instance of T in an aligned_storage::type object, whose bytes are set to zero, followed by a placement new. Hopefully the new value_init.hpp will make an end to the test failures. If so, I hope we can still merge the trunk version with the release version, 1.35.0. Kind regards, -- Niels Dekker http://www.xs4all.nl/~nd/dekkerware Scientific programmer at LKEB, Leiden University Medical Center