If you could make any changes to D, what would they look like?

Paul Backus snarwin at gmail.com
Mon Oct 25 18:59:51 UTC 2021

On Monday, 25 October 2021 at 18:22:59 UTC, IGotD- wrote:
> On Monday, 25 October 2021 at 18:12:36 UTC, Paul Backus wrote:
>> As far as I know this is not what `shared` does, and not what 
>> `shared` is intended to do. By itself, `shared` is just a 
>> marker for data that requires synchronization to access (what 
>> [the spec][1] calls "shared memory locations"). Whether that 
>> synchronization is accomplished using atomic operations or 
>> locking is entirely up to the programmer.
>> [1]: https://dlang.org/spec/intro.html
> Last time I tried a shared struct I had to cast away the atomic 
> operations on about every line. Is this removed in newer 
> compiler versions?

I think perhaps you are mistaking the suggestion to use atomic 
operations in the compiler's error message for the actual 
presence of atomic operations in the code.

shared int x;

void main()
     x += 1;
     // Error: read-modify-write operations are not allowed for 
`shared` variables
     //        Use `core.atomic.atomicOp!"+="(x, 1)` instead

The compiler requires you to use *some* kind of synchronization 
to modify `x`. The error message (perhaps misguidedly) *suggests* 
using atomic operations, but they are not actually required--you 
could also use a mutex.

If you're using a mutex, you do have to cast away `shared` once 
you have locked it, since in general the compiler has no way of 
knowing which mutex is associated with which variable.

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