Map.getOrDefault(Object,Supplier) override (original) (raw)

John Rose john.r.rose at oracle.com
Thu Apr 18 15:37:19 PDT 2013

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 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 x = myMap.getOrElse(myKey, Optional::of, Optional::empty); V y = (x.isPresent() ? x.get() : z);

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