Old problem with performance

[Andrei Alexandrescu]

Rainer Deyke wrote:
> Andrei Alexandrescu wrote:
>> The slicing problem exists in spades in this example, or better put its
>> converse (your code will fire asserts when it shouldn't). The reason is
>> rather subtle, so please try the code out to edify yourself.
> 
> You're referring to the automatically generated copy constructor in
> class 'avatar' which calls the copy constructor in class 'person',
> right?  That's a bug in my silly untested example code, but it's not the
> slicing problem.
> 
> Fix 1:
> 
> class person {
>   person(person const& org, bool allow_slicing = false) {
>     assert(allow_slicing || typeid(org) == typeid(*this));
>   }
> };
> 
> class avatar : public person, public deity {
>   avatar(avatar const& org, bool allow_slicing = false)
>     : person(org, true)
>   {
>   }
> };

So the problem exists since you are explicitly addressing it.

> Fix 2:
> 
> Trust the programmer to pay attention and remove the silly unnecessary
> assertion from class 'person'.
> 
> 

So the problem exists since you are trusting the programmer to avoid it.


Andrei