On Thu, 2010-03-18 at 16:40 +0100, Bert Freudenberg wrote:
> On 18.03.2010, at 16:30, Ralph Johnson wrote:
> > 
> > On 3/18/10, Bert Freudenberg <bert at freudenbergs.de> wrote:
> > 
> >> With true immutables you can start developing in a mixed object/functional style, which would allow interesting optimizations, e.g. for concurrency, memoization etc.
> > 
> > I've developed in a mixed object/functional style for years, and I
> > think a lot of other people do, too.   You don't need language support
> > for this, though I expect it would be helpful.  It makes concurrency
> > and distributed programming easier, and is important when you are
> > dealing with databases.  Eric Evans calls this "Value Object" in his
> > book "Domain Driven Design".
> > 
> > -Ralph Johnson
> 
> Right, the style is possible without VM support in your own subsystem. But being able to *guarantee* immutability would allow to generalize this beyond your own special-purpose code. And possibly it would enable further VM-level optimizations.

Even perfectly VM enforced immutability isn't enough to allow
optimisation if you still allow become:. It's always possible to swap
out the immutable object with a different one via become:.

Bryce