Immutable builder remove() method

[GoogleCodeExporter]

The builder classes which create instances of Immutable{Map,List,etc} 
should have a remove method, this would simplify the process of creating 
(for example) a map containing one less entry than an existing map.

The method:
ImmutableMap remove(ImmutableMap map, Object key) {
  HashMap m = new HashMap(map);
  m.remove(key);
  return ImmutableMap.copyOf(m);
}

could become:
ImmutableMap remove(ImmutableMap map, Object key) {
  return ImmutableMap.builder().putAll(map).remove(key).build();
}

Original issue reported on code.google.com by hartford...@gmail.com on 27 Oct 2009 at 10:12

[GoogleCodeExporter]

Our attitude toward this so far has been that it crosses the line toward 
overloading 
the builders with too much functionality. We don't want the builders to become 
poor-
man's collections. I think it's reasonable to have to do what you're doing 
currently 
... or the admittedly odd 

  ImmutableMap.copyOf(Maps.filterKeys(
      map, Predicates.not(Predicates.is(key))))

I'm not closing this yet, though.

Original comment by kevin...@gmail.com on 27 Oct 2009 at 10:22

[GoogleCodeExporter]

Original comment by kevin...@gmail.com on 5 Nov 2009 at 1:07

• Changed state: WontFix

[GoogleCodeExporter]

OK, I have a use case for this. I have a CopyOnWriteMap class that internally 
keeps an effectively immutable 
(volatile) map reference. When performing a mutating operation it takes a lock, 
then copies the map, modifies it, 
writes back the modified reference and then releases the lock. This works great 
for very fast read-mostly 
modestly sized caches.

I'd like to be able to use ImmutableMap (and ImmutableSortedMap) as the 
internal storage for these, but without 
the Builder supporting mutating methods I need two copies per mutator to 
achieve this.

Original comment by jed.wesl...@gmail.com on 18 Nov 2009 at 3:44