[External] : Re: ReversibleCollection proposal

[Remi Forax]

----- Mail original -----
> De: "Peter Levart" <peter.levart at gmail.com>
> À: "Stuart Marks" <stuart.marks at oracle.com>
> Cc: "core-libs-dev" <core-libs-dev at openjdk.java.net>
> Envoyé: Mercredi 12 Mai 2021 08:28:07
> Objet: Re: [External] : Re: ReversibleCollection proposal

> On 5/12/21 2:55 AM, Stuart Marks wrote:
>> As you point out, add() is kind of like addLast(), except without the
>> reordering semantics for LinkedHashSet. And reversed().add() is a
>> roundabout way of saying addFirst() -- also without the reordering
>> semantics for LinkedHashSet. I think most people's reactions would be
>> "Why didn't they just provide addFirst/addLast?" Plus the reordering
>> would be missing for LHS.
>>
>> A second-order issue is performance. I'd expect that implementations
>> would want to provide a fast-path for addFirst() that is amenable to
>> JIT optimization; this seems harder to achieve with reversed().add().
> 
> 
> The allocation of a reversed view instance typically goes away when C2
> compiles the method (if the instance isn't cached like in
> AbstractMap.keySet/values) so this can be as performant as specialized
> addFirst(), but lack of reordering of existent element in LinkedHashSet
> is a different problem I haven thought about.

Don't forget that the default method implementation is just that a default method,
at least the JDK implementations like LinkedHashSet can/should provide a better implementation.

> 
> 
> Regards, Peter

regards,
Rémi