std.concurrency and const

Christian Köstlin christian.koestlin at gmail.com
Wed Jan 5 22:22:19 UTC 2022


Hi all,

I really like std.concurrency but I now stumbled upon the following.
When receiving messages as const, they also need to be sent as const 
(otherwise they are not matched). Comparing this to normal function 
calls I would expect a different behavior.


```d
import std.concurrency;
import std.stdio;

struct Message
{
}

void fun(const(Message) m) {
     writeln("fun(const(Message))");
}
/*
void fun(Message m) {
     writeln("fun(Message)");
}
*/
void receiver()
{
     receive(
         (Tid sender, const(Message) m)
         {
             writeln("received const(Message)");
         },
         (const(Variant) v)
         {
             writeln("Received const(Variant)", v);
         },
         (Variant v)
         {
             writeln("Received variant", v);
         },
     );
     writeln("done");
}
int main(string[] args)
{
     auto blubTid = spawnLinked(&receiver);
     blubTid.send(Message());

     receive(
         (LinkTerminated t)
         {
         }
     );

     fun(Message());
     fun(const(Message)());
     return 0;
}

```

output is something like:
```
Received variantMessage()
done
fun(const(Message))
fun(const(Message))
```

whereas I would expect
```
received const(Message)
done
fun(const(Message))
fun(const(Message))
```

Looking forward for the explanation of that.


Kind regards and happy 2022!
Christian


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