C++ macro and templates

Question

Is there a way to pass

std::map<std::string, float>

as an argument to a macro?

(the problem is that the "," is used by the macro to split

std::map<std::string

and

float> 

as separate arguments. I would like to avoid this.

Answer 1

No, there isn't a way to do this, short of using a typedef. BOOST_FOREACH, for example, suffers the same problem.

Answer 2

Try to use a template instead of the macro.

Scott Meyers : Effective C++ Item 2: Prefer consts, enums, and inlines to #defines

Answer 3

Yes there is a way, it's indirect though.

As you have said, a macro is rather dumb in its interpretation. However it still recognize parenthesis.

Example: BOOST_MPL_ASSERT((boost::is_same<int,int>))

It works by using another level of parenthesis, thus forming a Tuple (from the macro point of view).

If you use the Boost.Preprocessor library, you can easily "unwrap" a Tuple to get its content unscathed. Unfortunately you are supposed to know the size of a tuple upfront, so you need an additional parameter

#define MY_MACRO(Size, TemplatedType, Name)\
  BOOST_PP_TUPLE_REM(Size)(TemplatedType) Name

And in action:

MY_MACRO(2, (std::map<int,std::string>), idToName);
    // expands to 'std::map<int,std::string> idToName'
idToName[1] = "Smith";

So, yes it is possible, but the macro has to be explicitly tailored to handle it.