[Issue 12491] New: [AA] Disallow non-`immutable` types as associative array keys

[d-bugmail at puremagic.com]

https://d.puremagic.com/issues/show_bug.cgi?id=12491

           Summary: [AA] Disallow non-`immutable` types as associative
                    array keys
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: verylonglogin.reg at gmail.com


--- Comment #0 from Denis Shelomovskij <verylonglogin.reg at gmail.com> 2014-03-30 12:18:35 MSK ---
Currently associative arrays are implemented with an assumption its keys hash
will not change. The only way to enforce it is to disallow non-`immutable`
(more correct not implicitly convertible to `immutable`) types as associative
array keys. E.g. `int` and `string` keys will still work, `const(char)[]` will
not.

This will cause a massive code breakage when e.g. mutable classes are used as
keys. Note such uses are potentially error-prone and incorrect but looks like
we have already inclined a lot of D users with such pattern.

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