Re: [boost] any

From: Peter Dimov (pdimov_at_[hidden])
Date: 2000-09-01 11:20:04

> >if(U * p = rx.is<U>())

> >if(rx.is<U>())

> Although source-level compatible, I think the naming may be a little
> misleading, but YMMV.

It is. to_ptr<U> is better in the first case, while is<U> is better in the
second.

>         any var;
>         ...
>         std::string text;
>         var.copy_to(text);

[versus]

>
>         if(std::string * converted = var.to_ptr<std::string>(var))
>             text = *converted;
>         else
>             ...

Yes, I see. So copy_to() can be implemented in terms of the public interface
of 'any' (to_ptr). Wouldn't this make it a candidate for a free function?

> >(2) typical type_info() usage.
>
> The following allows a simple sorting wrt type, and verification of
> result:
>
>         bool type_info_ordering(const any & lhs, const any & rhs)
>         {
>             return lhs.type_info().before(rhs.type_info());
>         }
>
>         void print_type_info(const any & to_print)
>         {
>             cout << to_print.type_info().name() << endl;
>         }
>
>         void sort_example()
>         {
>             vector<any> many;
>             ... // set up with values
>             sort(many.begin(), many.end(), type_info_ordering);
>             for_each(many.begin(), many.end(), print_type_info);
>         }
>
> The following demonstrates matching/filtering:
>
>         struct is_type : binary_function<any, const type_info *, bool>
>         {
>             bool operator()(
>                 const any & operand, const type_info * type) const
>             {
>                 return operand.type_info() == *type;
>             }
>         };
>
>         void find_example()
>         {
>             vector<any> many;
>             ...
>             vector<any>::iterator first_int =
>                 find_if(
>                     many.begin(), many.end(),
>                     bind2nd(is_type(), &typeid(int)));
>             ...
>         }

But note that the first example is already supported by ref<> (its op<
compares the types of the two objects) and the second can be easily done
with ref::is<int>, or any::to_ptr<int>. I was thinking of an example that
demonstrates the need for the type_info() function. Having a minimal
interface is good, isn't it?

--
Peter Dimov
Multi Media Ltd.