Possible to pass a member function to spawn?

Timon Gehr timon.gehr at gmx.ch
Tue Feb 7 15:53:57 PST 2012

On 02/08/2012 12:09 AM, Manu wrote:
> On 8 February 2012 00:33, Sean Kelly <sean at invisibleduck.org
> <mailto:sean at invisibleduck.org>> wrote:
>     On Feb 6, 2012, at 1:38 PM, Oliver Puerto wrote:
>      > Hello,
>      >
>      > I'm very new to D. Just started reading "The D programming
>     language". I should read it from beginning to end before posting
>     questions here. I know ... But I'm just too impatient. The issue
>     seems not to be that simple, nevertheless. The code below compiles
>     with Visual Studio.
>      >
>      > I want to have something like my actor class that I can start
>     running in it's own thread like in Scala or other languages that
>     support actors. So at best, I would like to do something like this:
>      >
>      >    MyActor myActor = new MyActor();
>      >    auto tid = spawn(&start, &myActor.run());
>     This should work:
>     void runActor(shared MyActor a) { (cast(MyActor)a)).run(); }
>     MyActor myActor = new MyActor();
>     auto tid = spawn(cast(shared MyActor) myActor, &runActor);
> See, my conclusion is, whenever using this API, you inevitably have dog
> ugly code.

If it is combined with OO.

> That code is barely readable through the casts... I can only
> draw this up to faulty API design.
> I understand the premise of 'shared'-ness that the API is trying to
> assert/guarantee, but the concept is basically broken in the language.

The concept is not broken at all. There are just too few type system 
features to conveniently support the concept.

> You can't use this API at all with out these blind casts, which is,
> basically, a hack, and I am yet to see an example of using this API
> 'properly'.

Passing value type and/or immutable messages works well.

> The casts are totally self defeating.

They indicate a potentially unsafe operation.

>     std.concurrency really should allow unique references to a
>     non-shared type to be passed as well, using something similar to
>     assumeUnique.
> Something like that should exist in the language (... or shared should
> just not be broken).

How would you improve usability of the shared qualifier without some 
kind of ownership type system?

> Using a template like assumeUnique is no better
> than the ugly cast. What does it offer over a cast?

Nothing. I prefer cast(immutable).

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