Re: [Boost-users] [fusion] Are Sequence stream IO operators recursive?

Subject: Re: [Boost-users] [fusion] Are Sequence stream IO operators recursive?
From: Hugh Dickinson (Hugh.Dickinson_at_[hidden])
Date: 2010-11-02 19:23:42

On 2 Nov 2010, at 20:05, OvermindDL1 wrote:

> On Tue, Nov 2, 2010 at 4:31 AM, Hugh Dickinson
> <hugh.dickinson_at_[hidden]> wrote:
>> I'm trying to output an adapted fusion sequence (PMT::QE::DataSet<PMT::QE::Measurement>) containing other adapted fusion sequences to std::cout. I had hoped for recursive behaviour, such that the contents of each sub-sequence are printed in turn. Having looked at the code in $BOOST_ROOT/boost/fusion/sequence/io/detail/out.hpp it looks like:
>> 
>> ----
>> PMT::QE::DataSet<PMT::QE::Measurement> output;
>> 
>> ... Fill output ...
>> 
>> std::cout << output << std::endl;
>> ----
>> 
>> should work. Unfortunately, I'm getting compilation errors like:
>> 
>> no match for ‘operator<<’ in ‘os << boost::fusion::operator* [with Iterator = boost::fusion::basic_iterator<boost::fusion::struct_iterator_tag, boost::fusion::assoc_struct_category, const PMT::QE::DataSet<PMT::QE::Measurement>, 0>](((const boost::fusion::iterator_base<boost::fusion::basic_iterator<boost::fusion::struct_iterator_tag, boost::fusion::assoc_struct_category, const PMT::QE::DataSet<PMT::QE::Measurement>, 0> >&)((const boost::fusion::iterator_base<boost::fusion::basic_iterator<boost::fusion::struct_iterator_tag, boost::fusion::assoc_struct_category, const PMT::QE::DataSet<PMT::QE::Measurement>, 0> >*)((const boost::fusion::basic_iterator<boost::fusion::struct_iterator_tag, boost::fusion::assoc_struct_category, const PMT::QE::DataSet<PMT::QE::Measurement>, 0>*)first))))’
>> 
>> The other errors simply replace the index 0 with 1 and 2 (PMT::QE::DataSet has 3 elements). On the other hand, the following does work:
>> 
>> ----
>> PMT::QE::DataSet<PMT::QE::Measurement> output;
>> 
>> ... Fill output ...
>> 
>> std::cout << at_c<0>(output) << std::endl;
>> std::cout << at_c<1>(output) << std::endl;
>> std::cout <<  at_c<2>(output) << std::endl;
>> 
>> ----
>> 
>> Is this the expected behaviour? What am I missing? Is there a way to achieve the desired recursive behaviour?
>> 
>> Many thanks,
> 
> You have included <boost/fusion/includes/io.hpp>, right?  Without that
> then output would generate an error like the above if output is a
> fusion sequence, else it should stream out fine.

Thanks for the reply. In answer to your question, yes, I've included that header. What confuses me the most is that the second example I gave works just fine, listing the contents of each of the 3 elements of "output". 

To offer some more (probably useless) information, I had not adapted the specialisation of PMT::QE::DataSet<PMT::QE::Measurement> but rather the generic PMT::QE::DataSet<T> using BOOST_FUSION_ADAPT_ASSOC_TPL_STRUCT. Since originally posting I've also tried adapting the specialisation and also making  PMT::QE::DataSet an ordinary non-template struct and adapting that with BOOST_FUSION_ADAPT_ASSOC_STRUCT. In all cases, I get the same error. 

Maybe this will help track down the problem.

Thanks again,

Hugh

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