Re: Mapping a constant its associated type using templates

"Tony Delroy" <>
Tue, 20 Mar 2007 02:54:29 CST

struct Column
     enum Type
         BOOL = 1,
         INT = 2,
         FLOAT = 3
         // so on and so forth

     Type getType(); // datatype of this column

Column* c = APIPtr->column("BID");

APIPtr->get(Column* c, int& val);
APIPtr->get(Column* c, char const*& val);
APIPtr->get(Column* c, double& val);

std::vector<Column*> columnCont;

I want to find a good way to iterate through the container, peruse the
type information already stored in the Column pointer (using the Type
enum) and extract the value of its fields. I am thinking it involves

You'll need explicit code to call the API...

for (vector<Column*>::const_iterator i = columnCont.begin();
     i != columnCont.end(); ++i)
    switch ((*i)->getType())
      case BOOL:
        bool x;
        APIPtr->get(*i, &x);
      case INT:
        int x;
        APIPtr->get(*i, &x);

You could optionally factor out some redundancy using a preprocessor
macro, but can't do much more than that. Having this switch though,
you can then dispatch the field handling in any way you like. For
example, you can use whatever polymorphic mechanism you like to handle
the different values (e.g. template <typename T>
do_somewthing_with(const T& value);, overloaded functions, put the
values into a variant class, call a preprocessor macro etc.).



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