Hi, Steven, Steven Watanabe wrote:
AMDG
Ad Majorem Dei Gloriam?
user_s_guide.html#id450311 line 363 accumulators.qbk line 189 for some reason external<> is not a link in the html
Ah, the link is broken. Thanks.
accumulators.qbk lines 35-37 [def _mpl_ [@../../libs/mpl MPL]] [def _mpl_lambda_expression_ [@../../libs/mpl/doc/refmanual/lambda-expression.html MPL Lambda Expression]] [def _parameters_ [@../../libs/parameters Boost.Parameters]] these links are bad
Thanks. I think I was overly-optimistic when I wrote that. The links would work if Accumulators were in it's rightful (a-hem) place in the Boost tree. ;-)
post_construct() Unless for some obscure reason that I am missing it is just too difficult, I would strongly prefer to make sure the constructors are called in the correct order.
The whole dance with fusion::vector is unnecessary. It would be simpler to use struct accumulator_tuple_base { template<class Args> accumulator_tuple(const Args&) {} } template<class T, class Base> struct accumulator_tuple : T, Base { template<class Args> accumulator_tuple(const Args& args) : T(args), Base(args) {} }; Since every accumulator is put before all the accumulators that depend on it in make_accumulator_tuple you can write typedef typename mpl::reverse_fold< sorted_accumulator_vector , accumulator_tuple_base , accumulator_tuple<mpl::_2, mpl::_1> >::type type; Then every accumulator is constructed after any others that it depends on. As a bonus the only limit to the number of accumulators is whatever the compiler can handle.
This would be a valid design choice, but it would involve reinventing a lot of Fusion. I use Fusion both to generate the accumulator set, to process the accumulators, and to find accumulators that match Fusion predicates. Code reuse is good. Regarding post_process(), I decided at the time, after discussing this with Joel de Guzman (of Fusion) and Dave Abrahams, that relying on the construction order of accumulators within a set would be a mistake. It would rule out size optimizations like compressed_pair, where empty accumulators are optimized away via the Empty Base Optimization. Fusion doesn't do this optimization today, but it may in the future.
What happens if you freeze a feature that another feature depends on? #include <iostream> #include <boost/accumulators/accumulators.hpp> #include <boost/accumulators/statistics/mean.hpp> #include <boost/accumulators/statistics/sum.hpp>
using namespace boost::accumulators;
accum_set; accum_set(1.0); accum_set(2.0); accum_set.drop<tag::sum>(); accum_set(3.0); std::cout << mean(accum_set) << std::endl; //prints 1 } This behavior can easily cause surprises. It must be fixed to print 2. I'm not quite sure how to implement it correctly. I think that probably you need to store the result at the point that drop is called for external lookup and continue to collect data for internal usage. Of course,
int main() { accumulator_set<double, features<tag::mean, droppable<tag::sum> this only applies in the face of dependencies.
The code is doing something a little unusual, but the result looks correct to me. What do you think the result should be, and why?
The user guide needs to specify what header each component is in.
Yes.
BOOST_PARAMETER_NESTED_KEYWORD.html There is no description of what this macro is for.
Thanks.
accumulator_set.hpp line 149 corresponds to -- What?
... a feature. Fixed.
accumulators_fwd.hpp #define's FUSION_MAX_VECTOR_SIZE/FUSION_MAX_TUPLE_SIZE This is a very bad idea as it might make make the value smaller than it would otherwise have been. Please just check FUSION_MAX_VECTOR_SIZE and issue a #error directive if it is too small.
I had it that way at first, but changed it due to user feedback. The idea is to make it so that you can just #define BOOST_ACCUMULATORS_MAX_FEATURES and not have to worry about configuring Fusion.
For simple cases at least the library seems to cause little to no overhead with msvc compared to hard coding everything.
Thanks for the report!
The docs need to state clearly what happens when more than one accumulator maps to the same feature.
Right. The first accumulator with a particular feature is the one that gets used. Any others with the same feature are ignored.
Overall the users guide is quite good. I had no difficulty understanding it. The reference manual is pretty sketchy though.
Good docs are always the hardest part.
For the most part the interface is clean and easy to use.
I definitely think Accumulators should be included in boost.
Thanks. -- Eric Niebler Boost Consulting www.boost-consulting.com