On Oct 10, 3:17 am, Christopher Schmidt wrote:

Am 10.10.2010 12:02, schrieb alfC:

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Hi,

...

 (I keep struggling with Boos.Fusion.)

...

 How do I deduce the type of the vector resulting from the transformation of another vector?

...

I have a source vector of different types, e.g. vectorsi::length, quantitysi::mass,    quantitysi::time

...

and I have a transformation that is well defined and returns another type depending on the original type. The question is how do I generate a vector type that is the result of the given transformation. I though that result_of::transform was the function to obtain the result but it turns not because it returns a type transform_view instead of a vector.

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vector< ... > v1; T? v2(transform(v1, transformation()));

...

i.e. what is the type of T as a fusion::vector as deduced from the type of v1 and the transformation type? -- Thank you,    Alfredo--

You can generate a vector from an arbitrary fusion sequence using the conversion metafunction:

http://www.boost.org/doc/libs/1_44_0/libs/fusion/doc/html/fusion/cont...

fusion::result_of::as_vector<         fusion::result_of::transform<                 v1,                 transformation         >::type

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::type v2(fusion::transform(v1, transformation()));

Hi, thank you. I tried something like this but I keep getting an error from the compiler. /usr/include/boost/utility/result_of.hpp:68: error: invalid use of incomplete type ‘struct divide::result{ typedef typename divide_typeof_helpersi::time >::type type; }; template<typename Q> typename result::type operator()(Q const& q) const { return q/quantitysi::time(1.*si::second); } }; It works well as a function but not as a metafunction in the following typedef typedef boost::fusion::result_of::as_vector< boost::fusion::result_of::transform< source_type, divide >::type >::type result_type ;

On Sun, Oct 10, 2010 at 12:09 PM, Christopher Schmidt wrote:

Am 10.10.2010 20:48, schrieb alfC:

...

On Oct 10, 3:17 am, Christopher Schmidt wrote:

...

Am 10.10.2010 12:02, schrieb alfC:

...

Hi,

...

 (I keep struggling with Boos.Fusion.)

...

 How do I deduce the type of the vector resulting from the transformation of another vector?

...

I have a source vector of different types, e.g. vectorsi::length, quantitysi::mass,    quantitysi::time

...

and I have a transformation that is well defined and returns another type depending on the original type. The question is how do I generate a vector type that is the result of the given transformation. I though that result_of::transform was the function to obtain the result but it turns not because it returns a type transform_view instead of a vector.

...

vector< ... > v1; T? v2(transform(v1, transformation()));

...

i.e. what is the type of T as a fusion::vector as deduced from the type of v1 and the transformation type? -- Thank you,    Alfredo--

You can generate a vector from an arbitrary fusion sequence using the conversion metafunction:

http://www.boost.org/doc/libs/1_44_0/libs/fusion/doc/html/fusion/cont...

fusion::result_of::as_vector<         fusion::result_of::transform<                 v1,                 transformation         >::type

...

::type v2(fusion::transform(v1, transformation()));

Hi, thank you. I tried something like this but I keep getting an error from the compiler.

/usr/include/boost/utility/result_of.hpp:68: error: invalid use of incomplete type ‘struct divide::result

what is the problem with the following transformation? that works well as a function but not as metafunction as called from result_of

struct divide{       template <typename SignatureT> struct result;       template<class Q>       struct result{               typedef typename divide_typeof_helpersi::time >::type type;       };       template<typename Q>       typename result::type               operator()(Q const& q) const       {               return q/quantitysi::time(1.*si::second);       } };

It works well as a function but not as a metafunction in the following typedef

      typedef               boost::fusion::result_of::as_vector<                       boost::fusion::result_of::transform<                               source_type,                               divide                       >::type               >::type               result_type       ;

Try const-qualifying source_type in fusion::result_of::transform<...> or add a specialization for a non-const reference argument type in divide::result. (fusion::transform just accepts a reference to a const-qualified sequence whereas fusion::result_of::transform does not care about const-qualification at all and passes the template parameter types right down to the fusion::transform_view .)

Yes, I just realized that something like that worked, a bunch of remove_const and remove_reference worked. Is there a way to simplify this? struct divide{ template <typename SignatureT> struct result; template<class Q> struct result{ typedef typename divide_typeof_helper< typename boost::remove_const< typename boost::remove_reference< Q >::type >::type, quantitysi::time >::type type; }; template<typename Q> typename result::type operator()(Q q) const { return typename result::type(); //return q/quantitysi::time(1.*si::second); } }; Thanks, Alfredo