Check the use of transformX instead of for_eachX

[headmyshoulder]

Check, if transform can be used instead of for_each in all algebras.

This must necessarily result in a new version of odeint, since it will break existing code.

[headmyshoulder]

It works in principle but it is difficult to use with boost::units. The result type of the transform-operations has to be determined from the operation:

template< class Fac1 = double >
struct scale_sum1
{
    typedef xxx result_type;     // what should xxx be for boost::units, or how can we determine xxx from Fac1, T1

    scale_sum1( Fac1 fac1 ) : m_fac1( fac1 ) { }

    template< class T1 >
    result_type operator()( T1 t1 ) const { return t1 * m_fac1; }

private:
    Fac1 m_fac1;
};

It would work with C++11 where one can use decltype.

[mariomulansky]

Hrm I would think there should be a way somewhere in boost units to obtain the result type of some unit-based operation. Maybe we could ask on the boost list?

[headmyshoulder]

Yes, I guess this is possible. But then we have to introduce another layer determining the result type of any operation.

[mariomulansky]

Or units_operations? Maybe the cleaner way to handle this rare use-case, although it would break existing code - but if we switch to transform anyhow this might be acceptable.

[headmyshoulder]

I think it would be a nice feature for the C++11 version of odeint. C++11 support decltype which is exactly what is needed here.

[mariomulansky]

so leave the switch to transform for the c++11 version?

[headmyshoulder]

Yeah, I think this is the best idea. Switching to transform is a large change, which cannot easily be done in the trunk since it breaks existing code.

[headmyshoulder]

Moved this issue in the feature wishlist in the wiki!