const?? When and why? This is ugly!

[Andrei Alexandrescu]

Walter Bright wrote:
> Steve Schveighoffer wrote:
>> Walter: Use invariant when you can, it's the best!
>> User: ok, how do I use it?
>> Walter: You need to cast mutable data to invariant, but it's on you to 
>> make sure nobody changes the original mutable data.  Casting 
>> circumvents the typesystem, so the compiler can't help you.
>> User: :(
> 
> Unfortunately, we could not come up with a typesafe scheme for going 
> from mutable to immutable that was reasonable. The transition is up to 
> the user to do correctly, but it isn't a terrible burden, and is simple 
> to get right.

In fact, since we last discussed that, dmd technology has made enough 
strides (particularly wrt manipulation of copies) that we can define 
Unique!T and something a la Java's StringBuilder with ease. 
Unfortunately current bugs in constructor implementation delay 
definition of such artifacts.


Andrei