Re: abstract unified interface

Daniel Wallin <[email protected]> writes:

> David Abrahams wrote:
>> Daniel Wallin <[email protected]> writes:
>> 
>>>I'm thinking we might need to make some decisions on the abstract
>>>unified interface thing since it will surely affect how everything else
>>>works.
>>>
>>>We need some ideas on how policies could be written language
>>>independently. One thing to notice here is that the conversion work will
>>>be done before any of the compile time generated converters get a chance
>>>to do anything. So I'm thinking maybe the callpolicies could get a
>>>chance to modify the function signature before the type_info's are
>>>produced.
>>>
>>>I think many policies could be expressed this way, for instance..
>>>
>>>   void f(const int*, int size);
>>>
>>>Could be transformed to:
>>>
>>>   void f(array_with_size<const int, int>);
>>>
>>>Given that the language backend has a converter registered for
>>> typeid(array_with_size<const int, int>), 
>> Seems reasonable
>> 
>>>which is of course somewhat of an problem.
>> Why?
>
> Because you'd have to explicitly register conversions for all
> combinations of the template parameters (well, not all.. but at least
> the once that you use). 

I would want to transform as much as possible (e.g. the size of that
array) into runtime values, wouldn't you?

> With compile time generated converters that are
> language dependent these kind of things are more convenient.
>
> This would maybe include things like transforming:
>
>    f(T*) [ adopt(_1) ]
>
> to
>
>    f(adopted_pointer<T>)
>
> I don't know.. 

Really?  I wouldn't have thought so.  I'd just build an AST of the
policies on the registration side and walk it with a visitor inside
the language-specific component.  Am I missing something?

> I'm just throwing out ideas here. There are some policies
> in luabind which I'm not sure can be done this way.. For instance we
> have a iterator_policy, which can handle conversions from stl containers
> to an iteratable sequence in lua. I think BPL has something similar (?).

We don't try to handle everything with a policy in BPL; this is one of
those things, though a policy might be better.

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



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