[boost] Re: Policy-based smart pointers revisisted (was: Re:Preliminarysubmission: command line & config file library)

From: David B. Held (dheld_at_[hidden])
Date: 2003-01-18 06:07:00

"Edward Diener" <eddielee_at_[hidden]> wrote in message
news:b0aro4$5gq$1_at_main.gmane.org...
> [...]
> I wonder if there have been any murmurs in the C++ standard
> committee about the system for setting default parameters somehow
> being changed to solve this problem, so that a user can override a
> default without having to override all preceding ones. I know I have
> heard suggestions about named default parameters but that doesn't
> seem to solve the problem in my mind. Something clearer and cleaner
> is needed but I don't know what it is.

Actually, the policy_ptr<> code in the sandbox features a policy adaptor
that automagically detects specified policies, and fills in defaults, in any
order.  However, it requires that the user specify policies using MPL
Lambda syntax.  And that still doesn't avoid the fact that non-default
configurations may require specifying several policies.  Finally, the
policy_ptr code has gotten too big for its own good, and has too many
templated c'tors that interfere with each other.  Frankly, I don't
understand all the issues with it any more.  I will probably try to write
tests for some more policy combinations, and then solicit help to figure
out how to make the conversion c'tors work.  They seem to be the last
and biggest hurdle.

As far as policy specification goes, perhaps a new idiom of building
policies into a unit, and passing them as one parameter might address
both the interface complexity issue and the default policy issue.  I think
it needs to be considered further.

Dave