[Boost-users] [phoenix][units] make boost.phoenix play well with boost.units

Subject: [Boost-users] [phoenix][units] make boost.phoenix play well with boost.units
From: alfC (alfredo.correa_at_[hidden])
Date: 2010-06-03 06:11:59

I have and expression of type

 arg1*arg1

which is contained in a deduced type LambdaExp (more preciselly
composite<multiplies_eval,vector<argument<0>, argument<0> >)

when trying to see what is the phoenix-deduced return type when input
is double

typename LambdaExp::template result<basic_environment<double> >::type

naturally, it gives 'double' (double*double)

but when the input type is a boost::units::quantity

typename LambdaExp::template
result<basic_environment<quantity<si::length> > >::type

it gives:

error_cant_deduce_type
(instread of the equivalent of quantity<si::area>, like in
quantity<si::area> a = quantity<si::length>()*quantity<si::length>() )

this is strange since it seemed that Phoenix  worked out of the box
with Units.

What is going on? How can we help Phoenix deduce the return type?
Does Phoenix need this help, like Boost.Lambda does by means of boost/
units/lambda.hpp?

Thank you,
Alfredo