Re: [boost] A small utility for template policy selection

From: David Greene (greened_at_[hidden])
Date: 2006-02-01 13:47:19

Sebastian Redl wrote:
> Spencer Collyer wrote:
> 
> 
>>Whilst working on a policy-based sparse-array class (which I hope to
>>submit to Boost at some point), I had the problem that there did not seem
>>to be any sensible way to organise the policies such that sensible
>>defaults could be coded in the template. Rather than always forcing the
>>users to specify the earlier policies, even when the default would be
>>fine, simply because they wanted to use a different policy for one of the
>>later parameters, I came up with the following little utility.
>
> This looks like a very nice utility, and I'm sure it could find application.
> A library facing a similar problem is the iterator library, where the 
> use_default mechanism was used. In this particular case, however, your 
> method is not applicable as it is, because the parameters specified by 
> use_default can be primitives.

The iterator library is different because it takes its template
parameters individually, not as an MPL sequence.  I'm working on
a Named Template Parameters library which would address the
needs of the iterator library.  It's fully functional (passing
400-some tests) but the documentation is lagging.

I literally just ran into a need for the policy selector this
morning and was going to quickly code something up but Spencer
beat me to it.  :)  I'd love to see something like this in
Boost.  It would complement NTP very nicely.

                        -Dave