Re: template function v.s. template class

From:

Ulrich Eckhardt <eckhardt@satorlaser.com>

Newsgroups:

microsoft.public.vc.language

Date:

Thu, 13 Dec 2007 08:49:26 +0100

Message-ID:

<6p4735-irf.ln1@satorlaser.homedns.org>

George wrote:

I am feeling template function is more tricky than template class. For the
reason that the compiler will do the matching automatically for template
function, but for template class, developer can assign how to match.

Sometimes compiler is doing mysterious matching rules for template
function, which makes us confused. Does anyone have the same senses? :-)

Example,

1. for template function

we define
[Code]
template <class T> void sort (vector <T>&)
[/Code]

when we invoke like,

sort (vector<int>)&, T will automatically matched by compiler to int

That doesn't even compile. Anyway: for a function, the compiler can deduce
the template parameters from the arguments (sometimes at least), while for
a class it can't. That's the reason that it is done for functions. However,
you can also explicitly specify the template parameters, e.g. if the
compiler is guessing wrong:

sort<int>(my_vector);

BTW: you could argue that the compiler could also guess the template
parameters for template classes sometimes. This is indeed true, but it is
simply not supported by the C++ standard, which is why compilers just don't
do it.

Uli