Comparator combinators

[Sam Pullara]

It was more a commentary on how often I would have to complicate the lambda expression than an actual suggestion. But I agree we can't do it for consistency reasons.

Sam

On Aug 21, 2013, at 2:23 PM, Joe Bowbeer <joe.bowbeer at gmail.com> wrote:

> > We could probably name that one comparing and name the other ones with their types, e.g. comparingObject.
> 
> This is the reverse of the way these are named elsewhere.  To be consistent, you'd need to rename IntStream as Stream, and Stream as ObjectStream.
> 
> I'd rather stick with an explicit Int where needed.
> 
> 
> On Wed, Aug 21, 2013 at 2:18 PM, Sam Pullara <spullara at gmail.com> wrote:
> I think the IntFunction version will be used more than any other
> version. We could probably name that one comparing and name the other
> ones with their types, e.g. comparingObject.
> 
> Sam
> 
> > On Aug 21, 2013, at 2:09 PM, Henry Jen <henry.jen at oracle.com> wrote:
> >
> > Seems the consensus is converging to disambiguate with the method name, which I am OK with. In fact, we had done that before and revert back because people don't like it.
> >
> > As mentioned several times, the not-intended boxing is the main concern. While I understand that IDE could help, I don't like to assume people will be using one(although most likely they are).
> >
> > How often will we need to add these explicit type? Is that type harder to figure out than knowing what we are comparing?
> >
> > Cheers,
> > Henry
> >
> >> On Aug 21, 2013, at 11:28 AM, Brian Goetz <brian.goetz at oracle.com> wrote:
> >>
> >> Waiting for input on this.
> >>
> >> I'm torn.  On the one hand, we'd be publishing a new, lambda-centric API that doesn't conform to our "safe overloading" rules, and for which users would have to use explicit lambdas in the cases where method references aren't practical.
> >>
> >> On the other, if we rename the primitive versions to comparingXxx/thenComparingXxx, we're creating a different sort of risk -- users will say
> >>
> >> comparing(Person::getAge)
> >>
> >> and get boxing when they didn't intend (this is comparing(Function<Person,Integer>), when they probably wanted comparingInt(ToIntFunction<Person>)).  Though this would be easy for IDEs to detect and suggest a replacement.
> >>
> >> I think the responsible thing to do is still probably to disambiguate by method name -- comparingInt, thenComparingLong, etc.  Which isn't pretty but seems to be the new equilibrium (overloading and inference are in opposition; adding more inference means we can tolerate less overloading.)
> >>
> >> If there's no input, an executive decision will be made...
> >>
> >>
> >>
> >>> On 8/14/2013 3:49 PM, Brian Goetz wrote:
> >>> This may well be our last API loose end...
> >>>
> >>> We currently have a pile of Comparator combinators, all currently called
> >>> comparing() or thenComparing().  Regardless of whether we choose to go
> >>> forward with the simplified overloading plan, these overloads have a
> >>> problem: for implicit lambdas, we can't distinguish between
> >>>
> >>>  comparing(T->U)
> >>> and
> >>>  comparing(T->int)
> >>>
> >>> because we don't type-check the body of the lambda until we do overload
> >>> selection, and don't do overload selection based on whether there are
> >>> type errors in the body (this was roundly rejected as being too
> >>> brittle).  So for lambdas like:
> >>>
> >>>  comparing(x -> x.size())
> >>>
> >>> we've got a circularity -- even under the older, more complex scheme.
> >>>
> >>> We'd thought perhaps that, if we adopted the heuristic that we can
> >>> eagerly give a type to method reference that refers to a non-overloaded
> >>> method (e.g., Person::getAge), then cases like
> >>>
> >>>  comparing(Person::getAge)
> >>>
> >>> can be handled, and this might take some of the pressure off the problem.
> >>>
> >>> For lambdas (with either approach) you can always get what you want with
> >>> an explicit lambda:
> >>>
> >>>  comparing((Person p) -> p.getAge())
> >>>
> >>> since this can be type-checked early.
> >>>
> >>> So the question is, is this good enough, even though it falls afoul of
> >>> the overloading guidelines for implicit lambdas?  Or, should we mangle
> >>> the names of the methods?
> >>>
> >>> This question comes down to whether we think its better to force
> >>> everyone to explicitly pick a method, but then supporting implicit lambdas:
> >>>
> >>>  comparingInt(x -> x.size())
> >>>
> >>> or forcing users to use non-ambigous method refs or explicit lambdas:
> >>>
> >>>  comparing(Person::getAge)
> >>> or
> >>>  comparing((Person p) -> p.getAge())
> >>>
> >>> Which disambiguation approach is worse?
> >
> 

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