Re: Copy of derived object from pointer to base

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From: Larry Brasfield (donotspam_larry_brasfield_at_hotmail.com)
Date: 10/12/04 

Date: Tue, 12 Oct 2004 09:37:43 -0700

"Sigurd Stenersen" <sigurds@utvikling.com> wrote in message news:%237Po%23fHsEHA.3588@tk2msftngp13.phx.gbl...
> Larry Brasfield wrote:
>> "Sigurd Stenersen" <sigurds@utvikling.com> wrote in message
>>> class Base
>>> {
>>> public:
>>> virtual Base *Clone() { return new Base(*this); }
>>> };
>>>
>>> class Derived : public Base
>>> {
>> #if 0
>>> virtual Base *Clone() { return new Derived(*this); } #endif
>>
>> virtual Derived *Clone() { return new Derived(*this); }
>>> };
>>
>> The reason to return a pointer whose type is pointer to the
>> derived class is to make the Clone() method usable, without
>> casting, when the result is known to be a subclass of Base.
>
> Sure, but that doesn't work on all compilers.

It works on all C++ compilers, (where 'C++' is as defined
by the current ISO standard).

> It certainly doesn't work on
> mine (VS6). Is it really legal C++ ?

Yes. There is even a name for this relationship among
methods along a class hierarchy, but I've forgotten it.

>> Proper support of this long time C++ feature came late
>> to MSVC++, arriving with v7.
>
> Ah, well. Does it allow for any return type, or just derived return types ?

The return type has to have the original (base) virtual
method's return type as a base class. 

-- 
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

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