typedeffing a partial specialization?

[Shriramana Sharma]

Hi -- in case of templates that take more than one parameter, I wondered if it would be possible to partially specialize it (if that's the correct technical term) and typedef it to something else, for example:

# include <iostream>
# include <vector>

template < typename T, unsigned int S >
struct tuple {
tuple () : vec(S) {}
T& operator [] ( unsigned int i ) { return vec.at(i) ; }
private:
std::vector<T> vec ;
} ;

template < typename T >
typedef tuple<T,2> pair<T> ;

However, the compiler complains saying:

typedef-template.cpp:13:20: error: no template named 'pair'; did you mean 'std:air'?

Apparently the following is one way to do it:

template < typename T >
struct pair : public tuple<T,2> {} ;

However I wonder, if I am able to do:
typedef tuple<double,2> twoDoubles ;

why can't I do:

template < typename T >
typedef tuple<T,2> pair<T> ;

 

[Victor Bazarov]

Hi -- in case of templates that take more than one parameter, I

wondered if it would be possible to partially specialize it (if that's
the correct technical term) and typedef it to something else, for example:

[...]

Look up "alias templates". I think you want

# include <vector>

template < typename T, unsigned int S >
struct tuple {
tuple () : vec(S) {}
T& operator [] ( unsigned int i ) { return vec.at(i) ; }
private:
std::vector<T> vec ;
};

template<class T> using pair = tuple<T,2>;

You need a compliant C++11 compiler for that, too.

V