IfThenElse template

[desktop]

I am trying to understand the use of this template and how to use it:
// Primary template.
template<bool C, typename Ta, typename Tb>
class IfThenElse;

// Partial specialization, true.
template<typename Ta, typename Tb>
class IfThenElse<true, Ta, Tb{
public:
typedef Ta ResultT;
};

// Partial specialization, false.
template<typename Ta, typename Tb>
class IfThenElse<false, Ta, Tb{
public:
typedef Tb ResultT;
};

int main() {
IfThenElse<true,std::string,intiff;
std::string str = iff.ResultT;
return 0;
}

When instantiated with true it should typedef the second argument
(std::string) to the public fieldResultT. But in main() I get an error
when I try to check the type of ResultT. Why is it not possible to
access ResultT?

[Markus Schoder]

On Sun, 13 May 2007 15:45:35 +0200, desktop wrote:

I am trying to understand the use of this template and how to use it:
// Primary template.
template<bool C, typename Ta, typename Tbclass IfThenElse;

// Partial specialization, true.
template<typename Ta, typename Tb>
class IfThenElse<true, Ta, Tb{
public:
typedef Ta ResultT;
};

// Partial specialization, false.
template<typename Ta, typename Tb>
class IfThenElse<false, Ta, Tb{
public:
typedef Tb ResultT;
};

int main() {
IfThenElse<true,std::string,intiff; std::string str = iff.ResultT;
return 0;
}

When instantiated with true it should typedef the second argument
(std::string) to the public fieldResultT. But in main() I get an error
when I try to check the type of ResultT. Why is it not possible to
access ResultT?

ResultT is a type so you must use it as a type:

int main() {
IfThenElse<true,std::string,int>::ResultT iff;
std::string str = iff;
return 0;
}

--
Markus Schoder

[desktop]

Markus Schoder wrote:

On Sun, 13 May 2007 15:45:35 +0200, desktop wrote:

>I am trying to understand the use of this template and how to use it:
// Primary template.
template<bool C, typename Ta, typename Tbclass IfThenElse;

// Partial specialization, true.
template<typename Ta, typename Tb>
class IfThenElse<true, Ta, Tb{
public:
typedef Ta ResultT;
};

// Partial specialization, false.
template<typename Ta, typename Tb>
class IfThenElse<false, Ta, Tb{
public:
typedef Tb ResultT;
};

int main() {
IfThenElse<true,std::string,intiff; std::string str = iff.ResultT;
return 0;
}

When instantiated with true it should typedef the second argument
(std::string) to the public fieldResultT. But in main() I get an error
when I try to check the type of ResultT. Why is it not possible to
access ResultT?

ResultT is a type so you must use it as a type:

int main() {
IfThenElse<true,std::string,int>::ResultT iff;
std::string str = iff;
return 0;
}

Ok but why does:

IfThenElse<true,std::string,intbbb;
bbb.ResultT;

or:

IfThenElse<true,std::string,intbbb;
bbb::ResultT;

work, it seems a bit more intuitive.

[Markus Schoder]

On Sun, 13 May 2007 20:14:41 +0200, desktop wrote:

Markus Schoder wrote:

>On Sun, 13 May 2007 15:45:35 +0200, desktop wrote:

>>I am trying to understand the use of this template and how to use it:
// Primary template.
template<bool C, typename Ta, typename Tbclass IfThenElse;

// Partial specialization, true.
template<typename Ta, typename Tb>
class IfThenElse<true, Ta, Tb{
public:
typedef Ta ResultT;
};

// Partial specialization, false.
template<typename Ta, typename Tb>
class IfThenElse<false, Ta, Tb{
public:
typedef Tb ResultT;
};

int main() {
IfThenElse<true,std::string,intiff; std::string str = iff.ResultT;
return 0;
}

When instantiated with true it should typedef the second argument
(std::string) to the public fieldResultT. But in main() I get an error
when I try to check the type of ResultT. Why is it not possible to
access ResultT?

ResultT is a type so you must use it as a type:

int main() {
IfThenElse<true,std::string,int>::ResultT iff; std::string str = iff;
return 0;
}

Ok but why does:

IfThenElse<true,std::string,intbbb;
bbb.ResultT;

Drop the typedefs in the template definition above and you get that
behaviour.

--
Markus Schoder