Boost C++ Libraries: Ticket #514: lexical_cast & pure virtual functions & VC 8 STL

redi — Fri, 18 Nov 2005 01:31:45 GMT

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The code is not valid, because the type of lexical_cast's
Source template argument must be CopyConstructible
http://boost.org/libs/conversion/lexical_cast.htm#lexical_cast

nobody — Tue, 29 Nov 2005 12:39:33 GMT

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Perhaps the a being a reference creates the confusion here?
The type of a is const & A.  And that (as a reference) is
copy constructible, even though A is not.

alnsn — Mon, 18 Sep 2006 15:29:16 GMT

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In my opinion, it is an important use-case. I'd change
requirements from
- Both Source and Target are CopyConstructible [20.1.3].
to
- Target is CopyConstructible [20.1.3].
- Source is CopyConstructible or, if not that,
  Source is polymorphic and the source value refers to an
object with dynamic type SourceDyn which is
CopyConstructible and operator<< called for Source is
equivalent to operator<< called for SourceDyn.

kevlin — Wed, 27 Sep 2006 12:39:24 GMT

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I do not believe that there is any longer a reasone that
Source needs to be restricted to being CopyConstructible.
There were reasons for this in the past, but those have
now passed and the requirements can be loosened so that
the only requirement on Source is that it is
OutputStreamable.
This would result in the requirements for the two
parameters being as follows:
  Source:
    OutputStreamable
  Target:
    InputStreamable &&
    CopyConstructible &&
    DefaultConstructible

alnsn — Tue, 16 Jan 2007 22:26:39 GMT

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Fixed in HEAD.
Affected files:
M ./boost/lexical_cast.hpp
M ./boost/detail/lcast_precision.hpp
M ./libs/conversion/lexical_cast.htm
M ./libs/conversion/test/Jamfile
M ./libs/conversion/test/Jamfile.v2
A ./libs/conversion/test/lexical_cast_abstract_test.cpp
Sergey, please check and close.

alnsn — Wed, 24 Jan 2007 14:39:01 GMT

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See also thread [boost] numeric_limits<Abstract> or how to fix 1358600?
http://lists.boost.org/Archives/boost/2007/01/index.php
especially John Maddock's proposal
http://lists.boost.org/Archives/boost/2007/01/115765.php
and my reply.

status changed

alnsn — Wed, 24 Jan 2007 14:42:29 GMT

status assigned → closed