Struggling to implement parallel foreach...

[Kagamin]

On Friday, 14 June 2019 at 01:40:46 UTC, Manu wrote:
> This has cascading issues; the closure contains references to 
> outer objects, but if the delegate is `shared`, then all those 
> references transitively inherit the shared attribute too. It 
> should work exactly like I if it was writing a `shared` method 
> to some struct, and all the members are shared... so the body 
> of the foreach needs to typecheck assuming the transitive 
> application of the inferred attributes from the opApply 
> signature.

Data attributes on delegates are not well supported because of 
https://issues.dlang.org/show_bug.cgi?id=1983

You have to construct the delegate and call the function in the 
usual way.

> As an experiment, I tried this:
>
> void test()
> {
>         int x;
>         void fun() shared
>         {
>             x++; // <-- error here
>         }
>         fun();
> }
>
> And I got this error:
>
> Error: `shared` function `test.fun` cannot access non-shared 
> data `x`
>
> That looks like a bug. `fun` is a delegate, and it's shared, 
> which means its `this` pointer is shared, which means `this.x` 
> should be shared... but that seems not to be the case.
>
> I think this is a bug. The compile error should have been that 
> I was
> unable to call fun() with a non-shared delegate (since the 
> calling
> scope is not shared).

Unqualified local variable is thread local and shouldn't be 
accessed by shared closure, because then it would be implicitly 
shared between threads.