Automatically create a clone() function for derived classes - comp.lang.c++

Message from discussion Automatically create a clone() function for derived classes

Sana

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More options Feb 20 2009, 2:47 pm

Newsgroups: comp.lang.c++

From: Sana <sanata...@gmail.com>

Date: Fri, 20 Feb 2009 06:47:44 -0800 (PST)

Local: Fri, Feb 20 2009 2:47 pm

Subject: Re: Automatically create a clone() function for derived classes

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On Feb 20, 9:25 am, Juha Nieminen <nos...@thanks.invalid> wrote:

> class Base
> {
> public:
> virtual Base* clone() const { return new Base(*this); }

> // other stuff here

> };

> The problem is that this clone() function must be replicated in all
> the derived classes as well, and their implementation is always the
> same, except for the type which is being allocated. For example:

> class Derived: public Base
> {
> public:
> virtual Base* clone() const { return new Derived(*this); }

> };

> It's not only tedious to have to write this line in each of the
> derived classes, but it's also error-prone: If you ever forget to add
> that line to some derived class, no compiler error will happen, and the
> program will even run, but when cloning a derived object using a base
> type pointer, you get a crippled copy, so the whole thing malfunctions,
> and it might malfunction in a very non-obvious way which is hard to
> track and debug.

Make the Base::clone() method pure and don't provide a body. this way,
if the derived class doesn't implement the clone() method, the linker
will complain.

virtual Base* clone() const = 0;

--
sana

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