A Sort Optimization Technique: decorate-sort-dedecorate

[neoedmund]

yeah, java also have 2 interface, Comparator and Comparable, which
equal to python's compareTo() and __cmp__()

Marc 'BlackJack' Rintsch wrote:
> In <1156723602.192984.49610 at m79g2000cwm.googlegroups.com>, Tom Cole wrote:
>
> > In Java, classes can implement the Comparable interface. This interface
> > contains only one method, a compareTo(Object o) method, and it is
> > defined to return a value < 0 if the Object is considered less than the
> > one being passed as an argument, it returns a value > 0 if considered
> > greater than, and 0 if they are considered equal.
> >
> > The object implementing this interface can use any of the variables
> > available to it (AKA address, zip code, longitude, latitude, first
> > name, whatever) to return this -1, 0 or 1. This is slightly different
> > than what you mention as we don't have to "decorate" the object. These
> > are all variables that already exist in the Object, and if fact make it
> > what it is. So, of course, there is no need to un-decorate at the end.
>
> Python has such a mechanism too, the special `__cmp__()` method
> has basically the same signature.  The problem the decorate, sort,
> un-decorate pattern solves is that this object specific compare operations
> only use *one* criteria.
>
> Let's say you have a `Person` object with name, surname, date of birth and
> so on.  When you have a list of such objects and want to sort them by name
> or by date of birth you can't use the `compareTo()` method for both.
> 
> Ciao,
> 	Marc 'BlackJack' Rintsch