Migrating methods in Collections

[Brian Goetz]

> interface AnyMap<K,V> { // ...
>     Optional<V> at(K key);
>     V at(K key, V defaultValue);
> }

An alternative to at(key, defaultValue) is tryAt(K, Consumer<V>) -- 
though the name tryAt is awful.  (I was considering map() and tryMap() 
as the new names for get().)

Just to put it on the record, Optional-bearing at() has a problem when 
the map can have null values -- but given that there are alternatives 
(default version, consumer version, legacy get()) in the cases where 
this might happen, I don't see this as a showstopper.

> For Queue, there's no good reason for having an Optional-returning
> method in addition to added default-returning version, so:

Why not?  Optional offers a lot of flexibility, since you have many 
options for what to do with the possibly-nonexistent value (orElse, 
orElseThrow, map, flatMap, ifPresent.)  Seems a natural building block, 
and a sharper tool than poll(defaultValue).