Hi all,
I was thinking of adding persistent collections to Groovy for quite a
while now. but I am wondering what library we should depend on here and
wanted to ask what you people generally use. Like pcollections, Guava,
functional Java, maybe stuff from Clojure or Scala?
Background:
persistent collection are collections (may or may not implement the
Collection interface) which cannot be modified later on. they have
nothing to do with persisting data in a database or on hard disc. They
are just more functional structures. Even though you cannot modify them,
you can combine the structure with new elements and get a new structure.
So a list+element will create a new list consisting of the old list and
the new element. But they will not just copy over data, they will reuse
the internal structure of the old list. A very simple form is that of a
filo stack. It can be a simple linked list of elements and we add the
new element in front, letting us to reuse the old list to almost 100%
and to create only a very small amount of new objects. There are of
course lists, sets and maps.
So why use them? Unlike unmodifiable made collections in Java, these
persistent collections are relatively safe to share between threads with
minimal synchronizations. Also, if you are working with functional
idioms they are more fitting the implicit assumptions of the data not
being modifiable.
Java collections are in general a bad fit here, since Collections are
more or less assumed to be modifiable. pcollections for example tries to
bridge that. In a Java8 world there is of course streams, which are a
much better fit in that.
bye blackdrag
- peristant and immutable collections Jochen Theodorou
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