Logical const

[Steven Schveighoffer]

On Fri, 03 Dec 2010 11:23:48 -0500, Bruno Medeiros  
<brunodomedeiros+spam at com.gmail> wrote:

> On 03/12/2010 13:22, Steven Schveighoffer wrote:
>  > I actually re-read the code and realized that it should work without  
> any
>  > changes (sans the issue you bring up below with implicit sharing of
>  > immutable).
>  >
>
> You mean if you wanted to pass a mutable object back and forth?
> No it wouldn't, if I understood you correctly. It would merely compile,  
> but not work (in the general case). So you would create an object, cast  
> it to shared (which means access would now need to be synchronized), and  
> pass it to another thread, right? However when you pass to another  
> thread the TLS part of the object state is lost (aka the _mutable part).  
> That might be valid for cached data that can be recalculated (like the  
> determinant), but it would not be valid for other kinds of mutable data  
> that the object would require and should not be cleared (like the parent  
> Widget in the other example you gave).

the mutable member is not marked as shared.  It cannot be accessed on a  
shared instance.  I guess it should be explicitly noted that a logical  
const notation (such as 'mutable') would not affect shared status, only  
const status.  shared does not implicitly cast to unshared or unshared  
const.

-Steve