Phil, that's an interesting point.
Consider (def x (cons (new java.util.Date) ()))
The object identified by x is *mutable*, but if the contained Date will not
be modified by the program, then the resulting object can be treated as
*effectively
immutable, *as you pointed out.
But, it would seem that you could pass x to another thread without
synchronization, and then safely read the contained Date instance by that
thread, because it has been safely published by virtue of having been
conveyed by a final field of the Cons instance. Of course, you would run
into trouble if you took that Date instance and passed it directly to
another thread without synchronization.
In other words, you could step outside of the limited profile of the Java
memory model that JCIP prescribes treating x as something (useful) between
*effectively
immutable *and *immutable, *with the end result being that you can treat x as
being *immutable.*
On Wednesday, May 7, 2014 7:13:31 AM UTC-4, Phillip Lord wrote:
>
>
> Since the data structures and interfaces, they are effectively
> immutable.
>
> Consider this:
>
> final public class Cons extends ASeq implements Serializable {
>
> private final Object _first;
> private final ISeq _more;
>
> public Cons(Object first, ISeq _more){
> this._first = first;
> this._more = _more;
> }
> }
>
> Although Cons uses final fields and constructor fields, "_more" is an
> ISeq; given that this could be mutable, so could cons.
>
> Phil
>
> Mike Fikes <mike...@me.com <javascript:>> writes:
>
> > Are the persistent immutable data structures in Clojure "truly"
> immutable
> > (using final fields, relying on constructor freezing), or are they mean
> to
> > be merely effectively immutable (as defined in JICP)?
>
> --
> Phillip Lord, Phone: +44 (0) 191 222 7827
> Lecturer in Bioinformatics, Email:
> philli...@newcastle.ac.uk<javascript:>
> School of Computing Science,
> http://homepages.cs.ncl.ac.uk/phillip.lord
> Room 914 Claremont Tower, skype: russet_apples
> Newcastle University, twitter: phillord
> NE1 7RU
>
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