Re: [boost] [Property Map] LvaluePropertyMapConcept problem

From: David Abrahams (dave_at_[hidden])
Date: 2006-09-05 09:33:49

"Stephan Diederich" <S.Diederich_at_[hidden]> writes:

> Hello,
>
> I'm having problems with the LvaluePropertyMapConcept.
> I expected that following code should compile:
>
> #include <boost/vector_property_map.hpp>
> int main(){
>   using namespace boost;
>   typedef vector_property_map<int> tSillyVecMap;
>   function_requires<LvaluePropertyMapConcept<tSillyVecMap, size_t> >();
> }
>
> Instead it bails out with an assertion from inside the LvaluePropertyMapConcept:
> Error: no matching call to »assertion_failed(mpl_::failed************
> boost::is_same<const int&, int&>::************)«
>
> It comes from that piece of code:
> template <class PMap, class Key>
> struct LvaluePropertyMapConcept{
> [snip]
> void constraints() {
>     typedef typename property_traits<PMap>::reference reference;
>     typedef typename property_traits<PMap>::value_type value_type;
>     BOOST_MPL_ASSERT((boost::is_same<const value_type&, reference>));
> [snip]
>
> Is that the intended behaviour?
>
> If not, where's the bug? Should property_traits<PMap>::reference be
> const, or should the Concept test against a const reference?

That doesn't look right to me.  I did some work on the concept
checking stuff recently, so I looked to see if I mis-translated the
original code, but AFAICT that's just what was in there from the
beginning.  Jeremy?

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com