Re: [boost] any

From: Kevlin Henney (kevlin_at_[hidden])
Date: 2000-09-03 06:26:56

In message <002b01c0158c$31c6f0e0$fe9560cb_at_yogi>, Mark Rodgers
<mark.rodgers_at_[hidden]> writes
>Very nice.  

Thanks.

>I did notice a couple of little things:
>
>1. Your operator= binds a non-const reference to a temporary in
>   the call to swap.  Please change to
>
>        any & operator=(const any & rhs)
>        {
>            any temp(rhs);
>            return swap(temp);
>        }

Oops! Well spotted and now fixed, thanks. Slack compiler and slack
author :->

>2. Your implementations of const and non-const versions of to_ptr
>   are the wrong way round.  In the const version, you cast away
>   constness leading to undefined behaviour.  You should put the
>   work in the const version and cast away the constness of the
>   return value in the non-const version.

They are fine the current way around and the behaviour is perfectly well
defined: You are not modifying a const object.

>3. I have a question mark over the implementation of to_ptr.  If
>   I write 
>
>      boost::any a(3);
>      const int *pi = a.to_ptr<const int>();
>
>   then it seems to me that I'll be casting content to 
>   holder<const int>, even though it's actually a holder<int>.
>   Perhaps you need to use remove_const from type_traits
>   in your cast.

It already works for this case. The type check is performed using the
result of typeid rather than dynamic_cast: dynamic_cast<holder<const
int> *> would fail but typeid(int) == typeid(const int) is true, so it
works as it stands -- no deconsting through traits is required.
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