Re: [Boost-users] [mpl][fusion] Metafunction for extracting a type from a map

From: Christian Henning (chhenning_at_[hidden])
Date: 2007-03-22 17:45:48

Hi there,

I think I was wrong when I was using a map. Instead I should have
presented my code using a vector. Here is another try to explain in
what I'm looking for. Image a 2D matrix of types. Meaning a vector of
types vectors. Like:

namespace fields
{
   struct id {};
   struct name {};
   struct address {};
   struct birthday {};
}

namespace tags
{
   struct pri {};
   struct val {};
}

typedef fusion::vector<fields::id, tags::pri> primary_key_t;
typedef fusion::vector<fields::name, tags::val> name_field_t;
typedef fusion::vector<fields::name, tags::val> address_field_t;
typedef fusion::vector<fields::name, tags::val> birthday__field_t;

typedef fusion::vector< primary_key_t
                      , name_field_t
                      , address_field_t
                      , birthday__field_t
                      > table;

My question is how can I find the type vector that contains a certain
type, like for example tags::pri?

Is such functionality supported by either fusion or mpl?

Thanks again,
Christian