[Boost-users] Re: Using MPL to write is_derived_from_std_basic_ostream

From: David Abrahams (dave_at_[hidden])
Date: 2004-09-02 15:19:12

"Jonathan Turkanis" <technews_at_[hidden]> writes:

> "Angus Leeming" <angus.leeming_at_[hidden]> wrote in message
> news:ch7h3d$466$1_at_sea.gmane.org...
>> I'm trying to ascertain whether a given class is, or is derived from,
>> std::basic_ostream, but I've ground to a halt.
>
> I've attached a somewhat improved version inspired by your attempt. (Thanks!) It
> only works on compilers which support has_xxx, but it should handle the case of
> private inheritance now, by delegating to is_base_and_derived.
>
> Note that with the current cvs it should not be necessary to write
>
>     mpl::and_< mpl::bool_<has_char_type<U>::value>, ...
>
> You can simply say
>
>     mpl::and_< has_char_type<U>, ...

It's hard for me to understand why you would need has_xxx for this
purpose, or how you would use it.

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com