Pure dynamic casts?

[Jarrett Billingsley]

On Tue, Sep 22, 2009 at 3:35 PM, Steven Schveighoffer
<schveiguy at yahoo.com> wrote:
> On Tue, 22 Sep 2009 14:03:28 -0400, Jarrett Billingsley
> <jarrett.billingsley at gmail.com> wrote:
>
>>
>> Or you could - I dunno - cache the result of the dynamic cast in a
>> local, since doing multiple dynamic casts is terrible style anyway.
>>
>> Just saying. ;)
>
> Yes, this is true of many optimizations :P
>
> Are you saying it's bad style because of the expense of dynamic casting or
> for some other reason?  If dynamic cast were pure, that takes away that
> argument.

Dynamic downcasts do usually indicate a weakness in the design. But an
even more fundamental matter of style is to not repeat yourself. You
don't use "x + y" if you need the sum of x and y in ten places; you do
"sum = x + y" and then use "sum." The same applies here. You're not
just working around a deficiency in the compiler, you're saving
yourself work later if you need to change all those values, and you're
giving it some kind of semantic attachment by putting it in a named
location.

Besides, you're probably going to be doing:

if(auto d = cast(Derived)baseRef)
{
    // ..
}

so you've already bound the result of the dynamic cast to a variable. *shrug*