Migrating methods in Collections

[Brian Goetz]

> One would think that the boxing of T would be an implementation of
> Optional<T>, which would be incompatibly different as a signature.

Right, that's the thinking towards "migrate map()V to one or more other 
method."  The existing map() is irretrievably null-polluted; write some 
new value-friendly methods.  One of the forms uses Optional; this 
assumes we can migrate Optional to be a value type in Valhalla 
(requiring additional migration tools, along the lines alluded to when 
you brought up collection index sizes.)

> Although I'm not exactly sure how this would work given the compromises
> defining Optional necessary to get it into jdk8.

Right.  As a reference type, Optional is a box, and so while more 
expressive than Integer, is no lighter.  As a value type, different story.