Re: [C++] Question on Templates (Vandevoorde & Josuttis)

From: Ulrich Eckhardt (doomster_at_knuut.de)
Date: 12/23/04 

Date: Thu, 23 Dec 2004 19:10:21 +0100

entropy123 wrote:

> Hi all,
>
> My question is related to 'Using Templates in Practice' section 6 of
> C++ Templates: Vandevoorde & Josuttis. I'm having trouble with the
> implementation of 'The Inclusion Model' for a class template. The
> example given by the authors is for a function template:
>
>>>From pg 62: The header file for the 'Inclusion Model':
>
> //declaration of template
> template <typename T>
> void print_typeof(T const&);
>
> //implementation/definition of template
> template <typename T>
> void print_typeof(T const& x);

Here the problems start: this is just a declaration, too!? I think you
either missed something or there is a mistake in the book. Check the
errata.

> As opposed to the 'Explicit Model:
>
> //explicity instantiate print_typeof() for type double
> template void print_typeof<double>(double const&);

If there was a definition of print_typeof in scope, this would instantiate
it for type double.

> Here is my header file for the 'inclusion model' database template. It
> does not compile and generates syntax errors along the line of " inT
> unidentified identifier" and so on:
>
> //InclusionBase.h
> template< typename T > class Base; //forward declaration
> template< typename T> class Base {}; //Base Template
> template <typename T> Base< T inT>; //?Implicit?
                               ^^^^^

What is the 'inT' supposed to mean there anyway? Sorry, but this syntax is
simply wrong. Please reread and try the examples in V&J first, before you
start modifying them.

> What do I need to do to implement an 'inclusion model' class template?
> Its just fine to explicitly define some of the derived classes, but I
> really would like to be able to allow Base<Datum> and Base<Type> to be
> replaced by something more generic....
>
> Please let me know if I need to clear anything up to get this question
> answered....

It might be interesting to know what exactly an 'inclusion model' is in
this context; I've never come across this term.

Uli 

-- 
FAQ: http://ma.rtij.nl/acllc-c++.FAQ.html

Relevant Pages