[rules-users] accumulate min over java.util.Date

[jkrupka]

A couple things..

Regarding not being able to write constraints against what's returned from
accumulate functions like min and max - in one particular use case (mine for
example) this would not be a big deal.  You are just trying to find the
min/max of a collection of objects that are comparable.  Not being able to
do things like match based on intValue > someValue for the returned Number
the way it currently does certainly would be a problem in some cases.

I don't know enough yet about how drools does the object type pattern
matching - so sorry if this is a dumb question =) , but if the accumulate
functions just return something of type Object or Comparable, is there any
way to do the from pattern matching like you can right now?  Could you
explicitly cast it somewhere?

The fact that you could do this (the min/max type functionality across any
comparable objects) with a custom accumulate function makes me think there
has got to be a generic way of doing it without writing custom accumulation
methods for each type... right?

Although, even though min and max would technically apply to Dates, things
like sum and average would not.  So maybe we could have a couple generic
min/max accumulate methods for anything comparable (which would allow you to
get the min/max if you don't care about any of the details), then ones
specific to Number (what exists right now), and possibly some more if there
are other types that have commonly used accumulate actions.

In one particular use
Wolfgang Laun-2 wrote:
> 
> 2011/3/25 Swindells, Thomas <TSwindells at nds.com>
> 
> >  I thought from was effectively typeless (as it’s operating against a
> List
> > it can’t always know the type of the members anyway) and so it allows
> any
> > type on teh left – giving a runtime class cast exception if it can’t
> do the
> > conversion. Therefore if you know they type you are expecting you can
> still
> > use it on the LHS with whatever constraints you want?
> >
> 
> Sure, "from" doesn't care what it produces, but accumulate
> functions have to
> return an object of some type. Currently. min and max return
> java.lang.Double; therefore you can use java.lang.Number as a portmanteau
> type. If min and max should include Data (and all other Comparable's), the
> actual result type will have to be Comparable (or Object).
> 
> -W
> 
> 
> >
> >
> > Thomas
> >
> >
> >
> > *From:* rules-users-bounces at lists.jboss.org [mailto:
> > rules-users-bounces at lists.jboss.org] *On Behalf Of *Wolfgang Laun
> > *Sent:* 25 March 2011 09:23
> > *To:* Rules Users List
> > *Subject:* Re: [rules-users] accumulate min over java.util.Date
> >
> >
> >
> > Now don't be hasty with a JIRA. Using Comparable for the arguments of
> the
> > min and max accumulate functions will give you a result that is --
> > Comparable. So:
> >
> >   $min: Comparable() from accumulate( Schedule( $d: date ), min( $d )
> )
> >
> > OK, this will give you the minimum data, bound to $min, although it
> won't
> > let you write any constraint for the "Comparable" result
> fact. But, what's
> > worse, it will not let you write
> >
> >   $min: Number( intValue > 100 ) from accumulate( X( $y: y ), min(
> $y ) )
> >
> > any more (unless I'm very much mistaken).
> >
> > -W
> >
> >
> >  On 25 March 2011 03:56, Greg Barton <greg_barton at yahoo.com>
> wrote:
> >
> > Well, if it can work that way it should.  I'd say open a JIRA and
> request
> > that feature.  It works with the "principle of least
> confusion." :)
> >
> >
> > --- On Thu, 3/24/11, jkrupka <jkrupka at gmail.com> wrote:
> >
> > > From: jkrupka <jkrupka at gmail.com>
> >
> > > Subject: Re: [rules-users] accumulate min over java.util.Date
> >
> > > To: rules-users at lists.jboss.org
> >
> > > Date: Thursday, March 24, 2011, 8:26 PM
> >
> > > Yea the docs weren't really clear
> > > about it, so I just thought it would work
> > > for anything that implemented Comparable =)
> > >
> > > Yep, used the long from getTime() - not the prettiest way
> > > of doing it, but
> > > it works great.
> > >
> > > Thanks!
> > >
> > > --
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