Re: Conversion policies

Daniel Wallin <[email protected]> writes:

>>I confess, though, that I am really confused about where this is
>>coming from, since I was sure you had agreed that "100% compile-time
>>converters" are not worth their costs.
>
> Yeah you're right, I did agree to that. I'm just trying to clear
> things up. ;) It is still unclear to me how runtime and compile time
> converters will interact though

Didn't we just say there weren't going to be any "compile-time
converters?"  Or did you mean something else?

> like in the case of our "adopt" policy.. In luabind it's a
> converter, in langbinding perhaps it will be a policy with a
> post-call action which removes ownership instead. I don't know..

Err...

I don't see how "it's a converter" vs. "it's a policy" is anything
more than a name game.  Ultimately it needs to do the same thing.  As
for whether ownership is removed post- call, it may be important to
choose pre-call removal in case an exception is thrown from the call
and the callee has already claimed ownership.

>> >
>> > The problem here is that the constructed temporary will be destroyed before
>> > it's returned from object_cast<T>(). Given that object_cast<T> is
>> actually a
>> > function rather than a type with implicit an cast to T of course..
>>
>>It's called "extract" in Boost.Python and
>>
>>      1. Yes, it's a type with an implicit conversion operator
>>
>>      2. Extraction of a reference to a temporary should fail at runtime
>
> Ok. Out of curiosity, why should it fail at runtime?

Because we can't make it fail at compile time?  It's clearly an error!

>> >> > One thing that would be cool is if you would be able to chain
>> >> > compile time selected converters with runtime dispatch
>> >> > converters.. Something like:
>> >> >
>> >> > chain(my_policy(result), default_policy)
>> >> >
>> >> > So that several converters can be tried even if you use a policy. Am I
>> >> > making sense here?
>> >>
>> >>Not yet.
>>
>>You gonna explain this stuff?
>
> Ok, I was just rambling about how compile time converters could
> interact with runtime converters. 

Still very confused as to why you'd ramble about something that we're
not doing  (?)

> I should have named "chain" "composite" instead; it tries all it's
> converters and returns a best match, just like the runtime system
> does.

Most confusing.

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



-------------------------------------------------------
This SF.net email is sponsored by: VM Ware
With VMware you can run multiple operating systems on a single machine.
WITHOUT REBOOTING! Mix Linux / Windows / Novell virtual machines
at the same time. Free trial click here:http://www.vmware.com/wl/offer/358/0