When is casting const() away actually necessary? (Used to be: Re: Why D const is annoying)

[Steven Schveighoffer]

On Wed, 02 May 2012 12:59:34 -0400, David Nadlinger <see at klickverbot.at>  
wrote:

> On Wednesday, 2 May 2012 at 16:52:33 UTC, Alex Rønne Petersen wrote:
>> shared? Almost always in any non-trivial application. shared is only  
>> useful if you're dealing with templatized functions that can actually  
>> handle it, which is not the case as often as one would like.
>
> Additionally, shared is currently little more than a marker for non-TLS  
> data.

No, it's very important that it is a type constructor.  For example, it  
makes weak-pure functions possible.

I think there is a large piece of shared missing/undefined, and that is,  
how do I mark something shared as "temporarily local".  I think Bartosz  
proposed something like "lent".

We essentially need the equivalent of const for shared.  Const unifies  
immutable and mutable, we need something to unify shared and thread-local.

The problem is, something like this needs to be combined with  
thread-locks.  I wonder if some kind of ARC would be useful for  
automatically unlocking the data.

-Steve