uniqueness propagation

[Tomek Sowiński]

Robert Jacques napisał:

> 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.

What were those difficulties?

-- 
Tomek