On 9/29/15 11:32 PM, Stephen Colebourne wrote:
In my view, the proposal is pretty good. I too use Guava's immutable
classes as types, because of the extra value obtained. But that does
not mean these methods should not be in the JDK. (Not every project
uses Guava).
Hi Stephen,
Thanks for looking at the proposal. I'm glad you like it.
I'd argue for two changes to the JEP.
Map.fromEntries() -> Map.ofEntries()
In JSR-310, we reserve "from" for factories with a high chance of
failure due to performing some kind of conversion, and use "of" for
factories that only fail if doing something stupid. It also means that
IDE users will easily see both choices when auto-completing, thus
easily learn how to go beyond the hard coded 6 entry factory.
Ah, this is quite helpful. I was mostly focusing on the "shape" of the
many-entries Map factory (varargs, builder, etc.) that I didn't think too much
about the name. I'll adopt your suggest of ofEntries().
Map.Entry.entry() -> Map.entry()
This would allow static imports to be focussed just on Map, and not
needing Map.Entry as well (helpful in Eclipse at least). If the method
were on Map.Entry, I'd expect it to be of(), whereas on Map itself,
entry() is a good name. There might be a case for having both
Map.entry() and Map.Entry.of().
Good. My current prototype already has the entry() convenience method on Map,
not Map.Entry. (I'm not sure, but earlier prototypes might have had it on
Map.Entry.)
My rationale for having the entry() method on Map is that it actually returns an
instance of Map.KeyValueHolder, a concrete implementation Map.Entry that's
intended to become a value class. The other obvious candidate implementation to
return is AbstractMap.SimpleImmutableEntry, which is problematic to turn into a
value class, as it's subclassable, has public constructors, and is serializable.
Soon, I'll post a webrev/specdiff/javadoc of the prototype so we can discuss
things more concretely.
s'marks
Stephen
On 30 September 2015 at 03:35, Stuart Marks <stuart.ma...@oracle.com> wrote:
Hi all, I've been on vacation for a few days. Did anything happen while I
was away? :-)
I see this JEP was posted as a Candidate, and Kevin and Remi had some
comments. I'll reply to Kevin's comments here and to Remi's separately.
Kevin,
I'm glad you don't think the proposal is bad. :-)
I definitely see the value in having immutability in the type system. If
your application is using Guava's immutable types, then it would certainly
be a step backwards to stop using them in favor of the factories proposed
here.
However, I don't see this JEP as being in opposition to immutable collection
types. This JEP isn't specifically about immutable collections; it's about
convenience APIs (some of which create collection instances that happen to
be immutable). Immutable collection types could be added later without too
much difficulty. I'd be interested in seeing and even possibly working on
such a proposal in the future.
Note that without permitting nulls, Map.of(key, Optional.of(value)) will
become
reasonably common, and that fact you can't serialize that will become even
more
strange than it already is.
Interesting. Given that Guava's Maps disallow null values, do you see a lot
of use of Optional for Map values in Guava? For the JDK, do you think it
would be preferable to allow null values in Maps, or to make Optional
serializable? (Note to readers: Guava's Optional is serializable but the
JDK's is not.) Or is this one of those problems where all the solutions
suck?
I think the example of "double-brace initialization" should be even more
clearly
labeled as pure evil. :-) You could also mention all the horrible
consequences
if anyone ever serializes such a collection.
I'm not sure if one is allowed to say "evil" in a JEP, but I agree that the
"double brace" "idiom" is definitely evil! I did mention the potential for
memory leaks in the JEP, but you have a good point about serialization, not
only of the enclosing instance, but also of all captured references.
s'marks
