[Issue 18985] bad error message for += operation on shared Object

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18985

RazvanN <razvan.nitu1305 at gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |razvan.nitu1305 at gmail.com

--- Comment #4 from RazvanN <razvan.nitu1305 at gmail.com> ---
AnyObject foo;
shared AnyObject bar;

void main()
{
    foo += 1; /* Error: foo += 1 is not a scalar, it is a object.Object */
    bar += 1; /* Error: read-modify-write operations are not allowed for shared
variables. Use core.atomic.atomicOp!"+="(bar, 1) instead. */
}

We can distinguish 4 situations here:

1. AnyObject does not define any opOpAssign methods => error message should be
in both situations "$object is not scalar"

2. Anyobject does define opOpAssign but it's not shared => foo passes
compilation, but bar does not and the most helpful error message would be
"read-modify-write operations are not allowed for shared variables. Use
core.atomic.atomicOp!"+="(bar, 1) instead or implement a shared opOpAssign for
type AnyObject"

3. AnyObject defines opOpAssign shared but not normal opOpAssign => foo += 1
fails with "object is not scalar message" and bar works.

4. AnyObject defines both shared/non-shared opOpAssign => both examples compile

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