Subject: Re: [boost] boost::mpl::for_each and value_initialized
From: Aleksey Gurtovoy (agurtovoy_at_[hidden])
Date: 2009-09-04 05:05:33
> what is the use of value_initialized in boost::mpl::for_each?
> It should be sufficient if the value is initialized by the constructor.
In theory, yes. In practice, at the time when the code was authored,
it wasn't -- see
> value_initialized() calls memset() in before calling the constructor.
Apparently this change was introduced in 1.35 release:
"New versions of value_initialized (Boost release version 1.35 or
higher) offer a workaround to these issues: value_initialized will
now clear its internal data, prior to constructing the object that
The fact that it's done unconditionally (as opposite only for compilers
with the discussed issues) is IMHO a bug.
> This memset() is not being optimized away with gnu-c++ 4.4.1.
My preferred way of addressing this would be to fix value_initialized by
#ifdef-ing the memset to be present for the faulty compilers only.
Could you verify whether the gcc will optimize away the rest of the
value_initialized magic if the memset is out?
-- Aleksey Gurtovoy MetaCommunications Engineering
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