poll for properties

[Andrei Alexandrescu]

Michel Fortin wrote:
> On 2009-07-28 19:59:30 -0400, Andrei Alexandrescu 
> <SeeWebsiteForEmail at erdani.org> said:
> 
>> The way Phobos does things is the following:
>>
>> a) You must define .empty which completes in O(1).
>>
>> b) If you can define .length with O(1), define it, otherwise don't.
>>
>> Then Phobos defines walkLength() on a best-effort basis which is 
>> guaranteed to finish in O(n) but may finish faster. It uses .length if 
>> defined, or else it just iterates the range to exhaustion.
> 
> This looks like a good approach. I'm just not too thrilled by the name 
> "walkLength". But perhaps I'm the only one.

STL defines distance() but people tend to forget it's O(n). So I chose a 
name that makes it rather obvious it's O(n).

Andrei