How to override opCmp when two different sorts are needed?

[Bill Baxter]

Jarrett Billingsley wrote:
> "John Bartelt" <bartelt at cox.net> wrote in message 
> news:f9quel$rou$1 at digitalmars.com...
>> I have a class that contains two variables. Sometimes I need to sort an 
>> array of the class based on variable 1, and later in the same progam sort 
>> the array based on variable 2.
>>
>> Can someone give me an idea of how to do this (smartly, efficiently, 
>> cleverly, polymorphically, ...)?
>>
>> Best idea that I've had so far is to use a static flag in the class to 
>> indicate which sort is desired, and then to have the overloaded opCmp() 
>> check the flag before comparing.
> 
> Write your own sort routine which takes a given predicate.  :\
> 
> Tango provides such a routine in tango.core.Array; phobos provides no such 
> analogue.  With phobos, either write your own routine, or use 
> std.c.stdlib.qsort.  I'll let you decide which is more elegant. 

There's also Oskar's sort w/predicate
     http://www.csc.kth.se/~ol/array.d

I thought the question was more about how to organize the software to 
control the change in behavior though.  For that I think you'll have to 
think about who "owns" the change in behavior and to whom the change 
should be visible to.

--bb