On Wed, 22 Sep 2004, Andre van Tonder wrote:

> There does not need to be any performance hit, since checking for
> immutability can and should be done, as it is in the reference
> implementation, at compile time.  Indeed, update! will give a compile-time
> error if a field does not support the update!.

An extremely obscure compile-time error.  This will be improved in the
next version.

Andre