Re: Templates and Copy Constructors. Again.

From: Victor Bazarov (v.Abazarov_at_comAcast.net)
Date: 02/23/05 

Date: Tue, 22 Feb 2005 21:34:08 -0500

"Matt Bitten" <mbitten73@yahoo.com> wrote...
> Now, what is it that is NOT a copy constructor, that has everyone so

Everyone? I'd probably refrained from speaking for *everyone*...

> confused? I read in the standard in 12.8 that a "template
> constructor" is not a copy constructor. However, a global search of
> the standard turns up no other use of the term "template
> constructor". So what is a template constructor?
> [...]
> It is not clear to me that this is what the standard says, however.

class Foo {
public:
    template<class T> Foo(T const& t); // a template constructor
};

template<class T> class Bar {
public:
    template<class U> Bar(const Bar<U>&); // a template constructor
};

The point is that in neither case the template constructor implements
or works in lieu of the compiler-generated copy constructor, although
you might think that if in the first case "T" is Foo, then the c-tor
becomes
         Foo(Foo const& t);

and in the second case if U is the same as T, then it becomes

         Bar<T>(const Bar<T>&);

The Standard says that it's not going to happen. In both classes Foo
and Bar<T>, the copy constructor that has a very specific signature
is going to be provided and will take over for all copy-construction
needs.

Victor

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