Re: Correct vesion (Re: Clone an object with an abstract base class)

From:

Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk>

Newsgroups:

comp.lang.c++

Date:

Sun, 12 Oct 2014 01:20:36 +0100

Message-ID:

<9MCdnYLHY6OjVKTJnZ2dnUU7-SOdnZ2d@giganews.com>

On 12/10/2014 01:18, Mr Flibble wrote:

On 12/10/2014 00:55, JiiPee wrote:

On 12/10/2014 00:26, JiiPee wrote:

How about checking the type of the *b object first and creating that
type of object:

void f2(B *b) {
    B *b1 = nullptr;
    if( typeid(*b).name() == typeid(D1).name() )
        b1 = new D1(*b1); // *b is type D1
    else if( typeid(*b).name() == typeid(D2).name() )
        b1 = new D2(*b1); // *b is type D2
}

and maybe also *b1 must be converted to its type like:
new D1( *((D1*)b1) )
?

this is better and compiles:

void f2(B *b) {
     B *b1 = nullptr;
     if( typeid(*b).name() == typeid(D1).name() )
         b1 = new D1(*(reinterpret_cast<D1*>(b1)));
     else if( typeid(*b).name() == typeid(D2).name() )
         b1 = new D2(*(reinterpret_cast<D2*>(b1)));
}

You should use static_cast not reinterpret_cast when casting from base
to derived.

Of course your solution doesn't scale: what if b points to an object
derived from D1?

Much better solution is to have a pure virtual clone() method.

/Flibble