Re: new Class(*this)

From:

Jorgen Grahn <grahn+nntp@snipabacken.se>

Newsgroups:

comp.lang.c++

Date:

11 Apr 2015 15:43:19 GMT

Message-ID:

<slrnmiig8l.2ot.grahn+nntp@frailea.sa.invalid>

On Thu, 2015-04-09, ?? Tiib wrote:

On Thursday, 9 April 2015 23:29:41 UTC+3, Jorgen Grahn wrote:

On Wed, 2015-04-08, ??? Tiib wrote:

On Thursday, 9 April 2015 01:25:18 UTC+3, Christopher Pisz wrote:

On 4/8/2015 4:01 PM, Doug Mika wrote:

On Wednesday, April 8, 2015 at 2:28:26 PM UTC-6, Doug Mika wrote:

I have the following two classes:

class Fish{
public:
virtual Fish* Clone()=0;
virtual void Swim()=0;
};

...

It is also unwise to implement such methods as "Clone". Silly methods
like those are often carried over from people who want to shape and mold
C++ to be like Java or wherever they came from. We don't need a clone
method, because we already have the means to make a copy...via the copy
constructor:

It is not silly. Sometimes we need dynamic polymorphism in C++.

Undoubtedly ... but the OP is obviously a newbie, and the things
you're talking about is (should be) an advanced and late topic.

It should be advised that if there is hierarchy with virtual
functions and if objects in such have to be copied at all
then 'clone' is idiomatically the best of choices.

I have to agree with Mr Pisz: I sense Java, or Smalltalk, or whatever,
lurking in the background here. Continuing that path is not a good
way to learn how to use C++ well.

Programmer has to have experience of debugging deep class hierarchy with
full yo yo of virtuals to realize how *not* to use C++ well. People
learn fastest from their own mistakes. Usage of other ways but
'clone' is one certain source of those headaches.

Ah, I see it now: he was critizising the clone(), not the
virtual-ness. You're probably right, then. (I have to admit I use
inheritance so rarely that I never had to fight slicing.)

/Jorgen

--
// Jorgen Grahn <grahn@ Oo o. . .
\X/ snipabacken.se> O o .