Subject: Re: [Boost-bugs] [Boost C++ Libraries] #6126: Signed integer members of Boost.Fusion adapted ADTs are not output correctly with Boost.Spirit.Karma rules
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-02-02 00:45:21
#6126: Signed integer members of Boost.Fusion adapted ADTs are not output
correctly with Boost.Spirit.Karma rules
-------------------------------+--------------------------------------------
Reporter: t0rt1e@⦠| Owner: hkaiser
Type: Bugs | Status: new
Milestone: To Be Determined | Component: spirit
Version: Boost 1.48.0 | Severity: Regression
Resolution: | Keywords: patch proposed, Boost.Spirit.Karma, Boost.Fusion, BOOST_FUSION_ADAPT_CLASS, BOOST_FUSION_ADAPT_ADT, short, int, long
-------------------------------+--------------------------------------------
Comment (by bugs@â¦):
I tracked it down to extract_from_attribute<>::call<>(attr,ctx,true_type).
It will generate an inner typedef of
typedef typename mpl::eval_if<
is_one_element_sequence
, detail::value_at_c<Attribute, 0>
, mpl::identity<Attribute const&>
>::type type;
which is going to be a reference. This is ok for tuples, adapted structs
(typical fusion sequences) but not for ADT's as the accessor function
returns a `short`, which **can** be bound to a const& **but** only locally
(its lifetime won't be extended outside the scope in which the reference
is declared).
Now the way I see it in the code, the sample from the docs[1] `(int, int,
obj.get_age(), obj.set_age(val))` won't work without undefined behaviour,
precisely because it results in `extract_from_attribute<>::call<>`
returning a reference to a local (`int` in that case).
For the OP, I guess the best way to fix it would be to make the accessors
return (const) references: (see attached)
struct XR
{
short x;
explicit XR(short num = 0) : x(num) {}
const short& getx() const { return x; }
short& getx() { return x; }
void setx(short v) { x = v; }
};
BOOST_FUSION_ADAPT_ADT(XR, (short&, const short&, obj.getx(),
obj.setx(val)))
This also removed all the other valgrind messages that were previously
unaccounted for.
[1]
http://www.boost.org/doc/libs/1_48_0/libs/fusion/doc/html/fusion/adapted/adapt_adt.html
-- Ticket URL: <https://svn.boost.org/trac/boost/ticket/6126#comment:13> Boost C++ Libraries <http://www.boost.org/> Boost provides free peer-reviewed portable C++ source libraries.
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