Sharing in D

[Steven Schveighoffer]

"Jason House" wrote
> Walter Bright Wrote:
>
>> Jason House wrote:
>> > Walter Bright Wrote:
>> >
>> >> http://www.reddit.com/comments/6u7k0/sharing_in_d/
>> >
>> > This is one of my 3 big wishes for the D language.
>> >
>> > The artical talks about shared being transitive just like
>> > const/invariant. I certainly hope it's more like pure than transitive
>> > invariant.
>>
>> Pure doesn't apply to data types, it applies to functions. I don't know
>> what you mean.
>
>
> Let's say I have an object that was originally written assuming non-shared 
> access and contains one member function with no arguments.  Some later 
> coder comes by and decides it'd be nice to share this object among threads 
> and creates a shared instance of it.
>
> There's no way to know if calling the member function is safe.  Maybe it 
> accesses a non-shared global variable.  Maybe a call to an encapsulated 
> object's member function uses a non-shared global variable.  The 
> maintainer must be extremely careful and scour the code to ensure there's 
> no accidental sharing that was not intended.
>
> Maybe I'm reading too much into stuff again, but the article did say "The 
> proposal is to make accidental sharing impossible".

I have a feeling that the shared/unshared comes with a requriement for 
'shared' functions.  That is, in order to call a function on an object that 
is 'shared', you have to call a function where the 'this' pointer is shared:

class C
{
   shared f(); // can call on a shared C instance, means the 'this' pointer 
is shared
   f(); // can call on an unshared C instance
}

-Steve