Re: operator==

"Daniel T." <>
Thu, 16 Dec 2010 08:10:20 -0500
Andrea Crotti <> wrote:

Obviously, if there is a batch of code that all op== functions have in
common, then you should write a function that takes care of that, but it
need not be an op==.

Why shouldn't it be op==?

Because you explicitly said you would never be comparing two objects of
different derived types. Giving the base class an op== implies that you
might do that.

Anyway now my code doesn't segfault anymore, the only problem I have is
that it calls
operator== from

class Serializable
    Serializable() {}
    virtual Stream toStream() const = 0;
    virtual bool operator==(const Serializable& other) { return false; };

and the thing is that if I make it pure then I have to change all the
operator== in the subclasses of Serializable, otherwise the signature is

That was what I was warning you about from the beginning. The signature
*is* different (whether the base class op== is pure virtual or not.)

Given something from
std::vector<Serializable *>

is it not possible to call the more specialized method of the object?

No, the compiler only checks the type of the left most object, the right
object is assumed to be a Serializable and so op==(const Serializable&)
is called every time which means (based on the code above,) that no two
Serializable objects are ever equal.

I mean if that pointer points to an object of a subclass of
Serializable, if I was able to call that operator== I would be fine and
everything would work...

Exactly why I told you your code wouldn't work.

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