how to assign to shared obj.systime?

[Arafel]

On 14/7/20 8:13, Kagamin wrote:
> ---
> import std;
> 
> shared class TimeCount {
>      void startClock() {
>          auto me = cast()this;
>          me.startTime = Clock.currTime;
>      }
>      void endClock() {
>          auto me = cast()this;
>          me.endTime = Clock.currTime;
>      }
>      void calculateDuration() {
>          auto me = cast()this;
>          me.elapsed = me.endTime - me.startTime;
>      }
> 
>      private:
>      SysTime startTime;
>      SysTime endTime;
>      Duration elapsed;
> }
> ---
> And this is shorter than your unshared member specification.

It won't work if you need to do it inside a struct instead of a class, 
because you'll get a copy:

```
import std;

shared struct S {
     void setA (int _a) {
         auto me = cast() this;
         me.a = _a;
     }
     int a;
}

void main() {
     shared S s;
     writeln("Before: ", s.a); // 0
     s.setA(42);
     writeln("After: ", s.a); // still 0
}
```

That said, `with (cast() this) { ... }` *will* work, because there's no 
copying. This is a really nice idiom that I didn't know and that I'll 
use from now on.

*However*, for this to work, you shouldn't use `shared` member variables 
unless absolutely necessary, much less whole `shared` classes/structs, 
and only declare the individual methods as shared, because casting away 
`shared` from `this` will only peel the external layer:

```
import std;

struct S {
     SysTime a;
     shared SysTime b;

     synchronized shared void setIt(SysTime t) {
         with(cast() this) {
             a = t;
             // b = t; // FAILS, `b` is still `shared` even for 
non-shared `S`
         }
     }
}
```

Also, I'm pretty sure there are still corner cases when you have to nest 
data structures, but so far this strategy seems good enough.