Re: [boost] any

From: Valentin Bonnard (Bonnard.V_at_[hidden])
Date: 2000-09-03 13:27:26

On Sun, Sep 03, 2000 at 09:48:21PM +1200, Mark Rodgers wrote:

> Very nice.  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);
>         }

Or 

any& operator= (any rhs)
{
  return swap (rhs);
}

> 2. Your implementations of const and non-const versions of to_ptr
>    are the wrong way round.

Everyone is free to program const-polymorphic code as he wish.

>    In the const version, you cast away
>    constness leading to undefined behaviour. 

Casting away constness never causes undefined behaviour.

It just makes it more easier to get.

>    You should put the
>    work in the const version and cast away the constness of the
>    return value in the non-const version.

Not necessarily.

> 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.

Or check the typeid of the holder instead of the object, to ensure 
that the static_cast is valid. By avoiding a call to a virtual function, 
you'll also gain some nano secondes.

-- 
Valentin Bonnard