[C++-sig] Re: Adding __len__ to range objects

[David Abrahams]

"Joel de Guzman" <djowel at gmx.co.uk> writes:

>> Then again, it also wouldn't work if v[1:4] was a wrapped
>> vector<element_proxy>, so why not just use a real Python list and save
>> some template instantiation work. Actually, I'm not sure whether
>> creating a working vector<element_proxy> wrapper might not mean more
>> programming work for us as well, in which case I'm definitely against
>> it :-)
>
> I am considering a slice_proxy<Container>. I am not sure how complicated
> the implementation will be, but I think this is the right solution to the problem.
> Schematically:
>
>     slice_proxy
>     {
>         Container& c;
>         Index from;
>         Index to;
>     };
>
> As for the foo (v[1:4])  problem, you can have an implicit conversion from
> a slice_proxy<Container> to a Container.

Consider whether this might be a way to save on template
instantiations:

    slice_proxy
    {
        object c;
        object from;
        object to;
    };

Remember, the container is already wrapped into a runtime-polymorphic
object ;-)

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