Map.getOrDefault(Object,Supplier<V>) override

[Jed Wesley-Smith]

> Optional<Map.Entry<K,V>> x = myMap.getAsOptional(myKey);
> V y = (x.isPresent() ? x.get().getValue() : z);

what's wrong with just using Optional:

myMap.getValueAsOptional(myKey).orElse(z)

or perhaps:

myMap.getAsOptional(myKey).map((Map.Entry<K, V> e) ->
e.getValue()).orElse(() -> z)

cheers,
jed.


On 19 April 2013 08:37, John Rose <john.r.rose at oracle.com> wrote:

> On Apr 18, 2013, at 2:45 PM, Brian Goetz <brian.goetz at oracle.com> wrote:
>
> > Feature creep alert!
> >
> > getOrDefault barely, and I mean barely, carried its weight.
>
> Putting on my lambdaphile hat again...
>
> I agree that getOrDefault is weak.  I suggest (what may already have been
> suggested?) the Supplier<T> version *instead* of the plain T version of
> getOrDefault.
>
> Then you could use Suppliers.constant(x) or
> Suppliers.alwaysThrow(IllegalArgumentException.class) or ()->(your code
> here).
>
>   int n = myToIntMap.getOrDefault(k, ()->Integer.MIN_VALUE);  // was
> .getOrDefault(k, Integer.MIN_VALUE)
>   String s = myMap.getOrDefault(k, ()->"none");  // was .getOrDefault(k,
> "none")
>   String t = myMap.getOrDefault(k, ()->{throw new
> IllegalArgumentException();});
>
> The current code for Functions.forMap has this comment which would be
> addressed by the more powerful getOrDefault:
>       // XXX mduigou it would be nice to optimise this to a single
> operation
>
> — John
>
> P.S.  Thinking about making this play with Optional led me to two bad
> options, which I'll float in case they inspire something better.
>
> #1 We could lean a little harder on the type Map.Entry.  Replace
> getOrDefault with:
>
>   class Map<K,V> {
>       Entry<K,V> getAsOptional(K key) { ... }
>    }
>
> Then:
>
>   Optional<Map.Entry<K,V>> x = myMap.getAsOptional(myKey);
>   V y = (x.isPresent() ? x.get().getValue() : z);
>
> #2 An extractor-based API would be powerful enough but too hard to use.  I
> mean something like:
>
>    class Map<K,V> {
>       R getOrElse(K key, Function<? super V,? extends R> ifPresent,
> Supplier<? extends R> ifAbsent) { ... }
>    }
>
> Then:
>
>   Optional<V> x = myMap.getOrElse(myKey, Optional::of, Optional::empty);
>   V y = (x.isPresent() ? x.get() : z);
>
>
>