uniqueness propagation

[Robert Jacques]

On Fri, 25 Feb 2011 02:48:01 -0500, Kevin Bealer  
<kevindangerbealer at removedanger.gmail.com> wrote:
> I think immutable could benefit from a Value Range Propagation-like  
> uniqueness

'unique' has been proposed and heavily discussed before in the news group.  
There even is std.typecons.Unique. Unfortunately, Walter has stated that  
there are issues/difficulties in adding 'unique' to the language.