[boost] Re: summary of casts.hpp suggestions

From: Darin Adler (darin_at_[hidden])
Date: 1999-09-19 23:39:17

>>     - polymorphic_downcast<> is poor name because it's for upcasts too
>>     + change name to polymorphic_static_cast<>
>
> Disagree. It's only for what I designed it for ;)
> Why would you use it for upcasts when implicit conversion does that
> automatically?

Oops! You're right! Sorry; I got confused.

Aside: It would be nice if a future implementation of polymorphic_downcast
contained a compile-time assertion that Derived is derived from Base, since
neither the static_cast nor the dynamic_cast requires that.

>>     - some users of casts.hpp may prefer asserts instead of exceptions
>>     + make version of casts.hpp that can do asserts instead of exceptions
>> (use two different namespaces and determine which to import into boost with
>> a compile-time switch; exception version should be default)
>
> Now you're talking about the numeric casts, right?

For someone that finds assertions that are removed from the final product
distasteful and prefers exceptions, I think that polymorphic_downcast<>
should be a synonym for polymorphic_cast<>. I don't see a major reason that
the runtime check should be elided in that particular case if you're a fan
of keeping in the runtime checks, even though dynamic_cast<> is more
expensive than static_cast<>.

Moving on, I'd typically use polymorphic_cast<> when I would otherwise use
dynamic_cast<>, but in cases where I know that the cast will succeed. I'd
prefer an assert to a runtime check just as I would in numeric casts, at
least for some projects.

So my intent there is to talk about all the casts.

    -- Darin