[External] : Re: ReversibleCollection proposal

[Peter Levart]

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.


Regards, Peter