Immutable Message Passing

[Jacob Carlborg]

On 2011-12-04 21:46, Andrew Wiley wrote:
> On Sun, Dec 4, 2011 at 1:42 AM, Jonathan M Davis<jmdavisProg at gmx.com>  wrote:
>> On Sunday, December 04, 2011 01:24:02 Andrew Wiley wrote:
>>> This should work, right? I'm not just going crazy or something?
>>>
>>> import std.concurrency;
>>> import std.stdio;
>>>
>>> class Bob {
>>> }
>>>
>>> void main() {
>>>      auto tid = spawn(&b);
>>>      tid.send(new immutable(Bob)());
>>> }
>>>
>>> void b() {
>>>      receive(
>>>          (immutable(Bob) b) {
>>>              writeln("got it");
>>>          }
>>>      );
>>> }
>>>
>>>
>>> I'm getting this from both GDC (trunk) and DMD (2.056 and trunk - I
>>> can't seem to get 2.055 to run):
>>> core.exception.AssertError@/usr/include/d/std/variant.d(286): immutable(Bob)
>>>
>>> Seems like some type conversion isn't working properly and variant is
>>> flagging immutable types as not assignable?
>>
>> Well, that particular assertion seems to be because of the immutability. It
>> seems that Variant can't handle it - the comment with it being
>>
>> // type is not assignable
>>
>> But I'd have to go digging to see why on earth this is failing (and that's
>> assuming that it's not a compiler bug, since then it would be completely out
>> of my league). It _looks_ like it should work.
>>
>> - Jonathan M Davis
>
> Actually, it looks like I am going crazy. I went back to dmd 2.052
> (and every version in between), and this doesn't seem to have ever
> worked.
> However, not allowing message passing with immutable messages
> eliminates one of the main use cases for immutable. I'll see if I can
> find a workaround.
>
> The actual issue is that once Variant finds a matching type, it tries
> to assign `immutable(Bob) = immutable(Bob)` , which is illegal.
> However, all it needs to do is assign a *reference* to an immutable
> object. Unfortunately, we don't support that.
> Incidentally, this makes a compelling argument for something like
> immutable(Object) ref.

Have message passing ever worked for other than primitive types 
(including strings) ?

-- 
/Jacob Carlborg