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From: bill@gibbons.org (Bill Gibbons)
Subject: Re: this-> required?
Date: 1998/04/29
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In article <354657D6.C45E924F@xilinx.com>, Lou Sanchez-chopitea
<lou.sanchez-chopitea@xilinx.com> wrote:

>     Is the following snippet of code correct?
> 
> template <class T> class Base
> {
> public:
>     int fBase ( void) { return 1;}
> };
> 
> template <class T> class Derived : public Base<T>
> {
> public:
>     int f1 ( void) { return fBase();}
>     int f2 ( void) { return this->fBase();}
> };
> 
>     In particular, is the this-> in f1 required? Thanks.
 
In article <3546960D.9B44837C@acm.org>, Pete Becker <petebecker@acm.org> wrote:

> Lou Sanchez-chopitea wrote:
> > 
> > 
> >     In particular, is the this-> in f1 required?
> 
> No.

Yes, it is.

The contents of "Base<T>" are NOT visible in the template definition
itself, because there is no guarantee that "Base<T>" will be an
instantiation of the template "Base".  It could be an instantiation
of an explicit or partial specialization.  The actual template from
which "Base<T>" is instantiated depeends on "T", which isn't known
until Derived<T> is instantiated.  In fact, "Base<T>" might not even
have a member "fBase" for a particular "T".

Some existing commercial compilers get this wrong.  They are attempting
to compile older code written before the template rules were completely
written (when templates were more like macros).  But such compilers can
actually generate incorrect code, and they encourage people to continue
writing ill-formed code such as that above.  So in my opinion vendors
which supply compilers that accept such cod are not doing their customers
a favor.


-- Bill Gibbons
   bill@gibbons.org


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