On Sun, 12 Sep 2010 09:35:42 -0400, Sönke Ludwig
<[email protected]> wrote:
9. unique
Unique objects or chunks of data are really important not only to be
able to check that a cast to 'immutable' is correct, but also to allow
for passing objects to another thread for computations without making a
superfluous copy or doing superfluous computation.
Unique (or for those with an Occam background 'mobile') has several
proponents in the D community (myself included). It was seriously
considered for inclusion in the type system, but Walter found several
issues with it on a practical level. If I recall correctly, Walter's exact
issues weren't made public, but probably stem from the fact that
unique/mobile types in other languages are generally library defined and
are 'shallow'. They exist as a 'please use responsibly' / 'here be
dragons' feature. For unique to be safe, it needs to be transitive, but
this severely limits the objects that can be represented. For example, a
doubly-linked-list can not be unique. Unique has been integrated into the
Clean and Mercury functional languages (or so says Wikipedia), so there
might be reasonable solutions to these problems.
