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c++templatesc++11typedeftr1

Typedef a template class without specifying the template parameters

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 what i've read so far, typedef'ing templates without arguments is not possible until official c++0x standard is available. So does anyone know an elegant workaround for this?

#ifdef _TR1
#include <unordered_map> 
typedef std::tr1::unordered_map MyMap; //error C2976: too few template arguments
#else
#include <map> 
typedef std::map MyMap; //error C2976: too few template arguments
#endif
Solution

  • 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++.