STL question. what is the difference...

[Michal]

Hallo Group Members

I unfortunatelly do not feel the difference between the 2 below.

namespace std {
template<typename T>
void swap(Widget<T>& a,
Widget<T>& b)
{ .... }
}


namespace std {
template<typename T>
void swap<Widget<T> >(Widget<T>& a,
Widget<T>& b)
{ .... }
}

Can You tell me what is the one?

best regards,
Michal

 

[Victor Bazarov]

I unfortunatelly do not feel the difference between the 2 below.

namespace std {
template<typename T>
void swap(Widget<T>& a,
Widget<T>& b)
{ .... }
}


namespace std {
template<typename T>
void swap<Widget<T> >(Widget<T>& a,
Widget<T>& b)
{ .... }
}

Can You tell me what is the one?

The former is the declaration and definition of the 'swap' template
function, the other is an attempt (currently illegal) to partially
specialise the existing template.

V

 

[Andrey Tarasevich]

I unfortunatelly do not feel the difference between the 2 below.

namespace std {
template<typename T>
void swap(Widget<T>& a,
Widget<T>& b)
{ .... }
}


namespace std {
template<typename T>
void swap<Widget<T> >(Widget<T>& a,
Widget<T>& b)
{ .... }
}

Can You tell me what is the one?

The second is not valid C++. Taking that into account, it is hard to
have a meaningful discussion about any other "differences" between the two.

 

[Michal]

The former is the declaration and definition of the 'swap' template
function, the other is an attempt (currently illegal) to partially
specialise the existing template.

V

conclusion: so if there is <....> after function name, then can I read
it as "specialization" (partial or total - whatever)?

 

[litb]

conclusion: so if there is <....> after function name, then can I read
it as "specialization" (partial or total - whatever)?

Yes. The result of an instantiation of a template is a function or a
class - depending on whether it was a function template or a class
template. That result is called specialization, because it's
specialized for that particular template parameter values. Sometimes
you write explicit specializations, if you don't want the compiler to
generate one for you out of the primary template (that generation
process is called instantiation) - for example because you want some
special handling to take place.

If you read <....> after a function name, it always refers to or
declares a specialization. Sometimes, it will cause instantiation of a
specialization from a primary template, and other times that
particular use declares an explicit specialization.

 

[Michal]

If you read <....> after a function name, it always refers to or
declares a specialization. Sometimes, it will cause instantiation of a
specialization from a primary template, and other times that
particular use declares an explicit specialization.

.... and what if I wrote it this way:
namespace std {
template<typename T>
void swap(Widget<T>& a,
Widget<T>& b)
{ .... }
}

Should it be read as some kind of "swap" function overloading, but
definitelly not any specialization or instantiation?

best regards,
Michal

 

[Andrey Tarasevich]

... and what if I wrote it this way:
namespace std {
template<typename T>
void swap(Widget<T>& a,
Widget<T>& b)
{ .... }
}

Should it be read as some kind of "swap" function overloading, but
definitelly not any specialization or instantiation?

This is indeed overloading, not a specialization or instantiation.