Re: [Boost-users] [Proto] Questions about deep_copy

Subject: Re: [Boost-users] [Proto] Questions about deep_copy
From: Kim Kuen Tang (kuentang_at_[hidden])
Date: 2009-05-10 15:52:36

Hi Eric,

thanks for your help.

I will try to integrate this in my code.

B/Rgds
Kim

Eric Niebler schrieb:
> Deep-copying only some terminals is fundamentally unsafe. 
> But if you really don't want to deep-copy the vector terminals, you'll 
> need to implement your own deep-copy algorithm. It's easiest to write 
> a grammar with transforms that does it for you.
>   #include <vector>
>   #include <boost/proto/proto.hpp>
>
>   namespace boost { namespace proto
>   {
>       // make std::vector a proto terminal extension
>       template<typename T, typename Al>
>       struct is_extension<std::vector<T, Al> >
>         : mpl::true_
>       {};
>   }}
>
>   namespace proto = boost::proto;
>   using proto::_;
>
>   // Deep-copy all terminals except vectors
>   struct DeepCopyNotVectors
>     : proto::or_<
>           proto::when<
>               proto::terminal<std::vector<_,_> >
>               // The vector itself will be held by reference, but the
>               // temporary proto terminal expression wrapping the
>               // reference should be held by value.
>             , boost::remove_const<boost::remove_reference<_> >(_)
>           >
>         , proto::when<proto::terminal<_>, proto::_deep_copy(_)>
>         , proto::otherwise<
>               proto::nary_expr<_, proto::vararg<DeepCopyNotVectors> >
>           >
>       >
>   {};
>
>   int main()
>   {
>       using namespace proto::exops;
>
>       std::vector<int> a, b;
>
>       BOOST_AUTO(tmp0, a + b + 0.1);
>       BOOST_AUTO(tmp1, DeepCopyNotVectors()(a + b + 0.1));
>
>       std::cout << typeid(tmp0).name() << "\n\n";
>       std::cout << typeid(tmp1).name() << "\n";
>   }
>
>   int main()
>   {
>       using namespace proto::exops;
>
>       std::vector<int> a, b;
>
>       BOOST_AUTO(tmp0, a + b + 0.1);
>       BOOST_AUTO(tmp1, DeepCopyNotVectors()(a + b + 0.1));
>
>       std::cout << typeid(tmp0).name() << "\n\n";
>       std::cout << typeid(tmp1).name() << "\n";
>   }
>
>
>