[dmd-concurrency] Defining shared delegates

[Andrei Alexandrescu]

Robert Jacques wrote:
> On Tue, 19 Jan 2010 16:20:43 -0500, Andrei Alexandrescu 
> <andrei at erdani.com> wrote:
>> Michel Fortin wrote:
>>> Le 2010-01-19 à 15:20, Andrei Alexandrescu a écrit :
>>>
>>>> One suggestion about shared delegates: should we take the executive 
>>>> decision to not define them at all? There's nothing you can do with 
>>>> delegates that you can't do with classes. Although generally 
>>>> delegates do justify their existence because they're more comfy than 
>>>> e.g. local classes, it doesn't strike me as obvious we'll need 
>>>> comparable convenience when dealing with shared classes.
>>>  The reason I wrote all this is because I think delegates can be much 
>>> easier to work with than classes. That's what I tried to demonstrate.
>>>  That's because delegates completely encapsulate the "sharedness" of 
>>> what they touch, which means that contrary to other types you can 
>>> implicitly convert a shared delegate to a thread-local one. This 
>>> should make them much easier to share than most other types, 
>>> including classes.
>>
>> I may be missing something, but passing a delegate object across 
>> threads begets arbitrary sharing of that delegate's state across 
>> threads - because the delegate can do anything to its data. In fact, 
>> many functional languages define poor man's classes as delegates that 
>> dispatch the action depending on arguments. There are examples in e.g. 
>> SICP (http://mitpress.mit.edu/sicp/).
>>
>> Andrei
> 
> Yes, I believe you are. You described a regular delegate that is shared 
> between threads. What Michel and I have been talking about is a shared 
> delegate, which can be safely passed between thread. A good example of 
> what a shared delegate would be is the member function of a shared 
> class, while a regular delegate is the member function of a normal 
> class. i.e. the delegate's state would be protected in the same way any 
> other shared object would be.

I understand now. So is it correct to assess that if we get the rules 
for classes straight we also have delegates covered?

Andrei