design question

[BCS]

Reply to Andrei,

> Walter Bright wrote:
> 
>> Andrei Alexandrescu wrote:
>> 
>>> keepStable is a template function that simply wraps the range in a
>>> different type. It's a way to pass information about the range
>>> (e.g., "keep this stable", or "this is sorted already"), to the
>>> function understanding it.
>>> 
>> Would these be composable? I.e.:
>> 
>> thisAttribute(thatAttribute(T)) is the same as
>> thatAttribute(thisAttribute(T)) ? Would the algorithm detect the
>> 'inner' attribute?
>> 
> Great question. Not sure whether I can implement composition to be
> entirely order-invariant, but yes, the algorithm should "see" various
> attributes of the wrapped range.
> 
> Andrei
> 

you could do composition by tuple/set unioning and always sort the set (by 
.stringof)