Help with non-const first_type in std::map

[Paul Dubuc]

Question: In the following template function signature

template <class MAP>
int matchAbbreviationMap(
const MAP & choices,
typename MAP::value_type::first_type & arg,
typename MAP::value_type::second_type & val)
{
...

MAP is a std::map or std::multi_map so MAP::value_type::first_type is a const
type. I want arg to have the same type but to be non-const. Is there some
way to do this generically without specifying a redundant type in the template
parameters?

Thanks,

 

[Victor Bazarov]

Question: In the following template function signature

template <class MAP>
int matchAbbreviationMap(
const MAP & choices,
typename MAP::value_type::first_type & arg,
typename MAP::value_type::second_type & val)
{
...

MAP is a std::map or std::multi_map so MAP::value_type::first_type is
a const type. I want arg to have the same type but to be non-const. Is
there some way to do this generically without specifying a
redundant type in the template parameters?

You could try this:

// auxiliary templates for type extraction
template<class T> struct drop_const { typedef T type; };
template<class T> struct drop_const<T const &> { typedef T type; }

..
template<class MAP>
int match...
typename drop_const<MAP::value_type::first>::type & arg,
...

Or some such.

V