[boost] Re: What I Hate About How We Abstract System Dependence

From: David Abrahams (dave_at_[hidden])
Date: 2005-03-08 09:49:39

Rob Stewart <stewart_at_[hidden]> writes:

> From: David Abrahams <dave_at_[hidden]>
>> Rob Stewart <stewart_at_[hidden]> writes:
>> > From: David Abrahams <dave_at_[hidden]>
>> >> 
>> >> I have always thought that concrete implementations of portable
>> >> libraries should supply users a way to get at the OS-specific data so
>> >> they can use platform-specific facilities on them if neccessary.
>> >
>> > Exactly what I was thinking.  That's all it takes, but you don't
>> > want to make it syntactically quiet to get at the underlying
>> > OS-specific data.  IOW, you want something akin to the new-style
>> > casts in verbosity so the switch to non-portable code is loud and
>> > clear.
>> >
>> > Doing that via a derived class is one way.  Using a cast to the
>> > OS-specific type within the portable facade is another.  (The
>> > latter doesn't introduce polymorphic side effects such as call
>> > overhead or slicing.)
>> >
>> > boost::whatever w;
>> > special_type s(boost::platform_cast<special_type>(w));
>> >
>> >> You have to understand, the Boost.Threads specification was designed
>> >> to become a standard, and as such it didn't include anything
>> >> nonportable.  That said, there's no reason we shouldn't expose the
>> >> low-level thread IDs and document them in a special section on
>> >> platform specifics.
>> >
>> > If the platform specifics are kept from the portable interface --
>> > through implementation magic -- then we get both properties.
>> 
>> I think that's much too fancy.  Put a free function to access the
>> platform-specific data in a separate header and you're done.
>
> special_type == platform-specific data
> platform_cast == free function
>
> What's "much too fancy" in my suggestion?  I didn't mention a
> separate header, but there's little difference otherwise.

You mentioned "implementation magic."
I thought you had something elaborate in mind.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com