Typedef a template class without specifying the template parameters

Question

I\'m trying to typedef either an unordered_map or std::map depending whether there are TR1 libraries available. But I don\'t want to specify the template parameters. From wh

Answer 1

You have to use full types for typedefs.

Use a #define macro instead.

Answer 2

The way I've seen this done is to wrap the typedef in a template-struct:

template<typename KeyType, typename MappedType>
struct myMap
{
#ifdef _TR1
    typedef std::tr1::unordered_map<KeyType, MappedType> type;
#else
    typedef std::map<KeyType, MappedType> type;
#endif
};

Then in your code you invoke it like so:

myMap<key, value>::type myMapInstance;

It may be a little more verbose than what you want, but I believe it meets the need given the current state of C++.