[boost] Re: [range] update on ADL hooks

From: David Abrahams (dave_at_[hidden])
Date: 2005-03-25 03:25:13

Thomas Witt <witt_at_[hidden]> writes:

>> Yes, the whole area of dispatching and customization of generic
>> functions is nasty in C++.  I've known it's problematic for a long
>> time, but had a hard time expressing how bad the problem is in a way
>> that would communicate to someone who doesn't do heavy generic
>> programming day in and day out.
>
> I agree that something needs to be done. I just really want to be 
> convinced that the proposed changes to boost::begin are the right solution

Without going into the description of the language problems too
deeply, here's a prototype of what Doug and I came up with.  So far it
only compiles for me with g++.

Things to notice:

- ADL is limited to *one* name, lookup_implementation()

- ADL is decoupled from the actual types being passed to algorithms
  via their category tags

- You can write generalized lookup_implementation() functions like the
  one shown, that choose some rules by which to dispatch all
  algorithms

- You can write specific lookup_implementation functions to set
  different rules for particular algorithms.



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