[Issue 8157] New: Disallow (dis)equality among two different enums

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=8157

           Summary: Disallow (dis)equality among two different enums
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: bearophile_hugs at eml.cc


--- Comment #0 from bearophile_hugs at eml.cc 2012-05-28 13:57:33 PDT ---
This enhancement request is related to Issue 3999 but it's not the same
problem.

Issue 3999 asks to statically disallow:

enum E1 { A, B }
enum E2 { C, D }
void main() {
    E1 a;
    assert(a == 0);
}


While this issue asks to statically disallow:

enum E1 { A, B }
enum E2 { C, D }
void main() {
    E1 a;
    assert(a == E2.C);
    assert(a != E2.C);
}


(Well, Issue 3999 asks to disallow both cases, so this issue is a subset of
Issue 3999 .)


Discussion:
http://forum.dlang.org/thread/lyzudurkvguonbmmjqfp@forum.dlang.org

See an answer by Andrei Alexandrescu:
http://forum.dlang.org/thread/lyzudurkvguonbmmjqfp@forum.dlang.org#post-jpvvm2:242d8l:241:40digitalmars.com

> I do agree that it's wrong to _conflate_ the enumerated value with it 
> ordinal, so in this program neither comparison should compile without an 
> explicit cast:
> 
> enum E1 { A, B }
> enum E2 { C, D }
> 
> void main() {
>     E1 a;
>     assert(a == 0);
>     assert(a == E2.C);
> }
> 
> The first one is probably difficult to disallow at this time, but the 
> second one almost always indicates a bug, confusion, or abuse on the 
> user side. We should disallow it.

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