[Issue 12420] [AA] Can't set associative array with array as key value using key type

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=12420

Kenji Hara <k.hara.pg at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |INVALID

--- Comment #4 from Kenji Hara <k.hara.pg at gmail.com> ---
(In reply to Denis Shelomovskij from comment #3)
> Looks like you misunderstood me. The word `immutable` shouldn't be here,
> it's just an incorrect error message. Currently we have no rules disallowing
> non-`immutable` associative array keys. I filed Issue 12491 for this.
> 
> This issue will be auto-fixed if Issue 2954 will be fixed by applying a
> correct check to ensure key expression can be implicitly converted to AA key
> type in case of setting AA value.

In D, AA requires immutability for the key. In evidence all AA key types are
implicitly qualified with const.

    int[char[]] aa;
    pragma(msg, typeof(aa));    // Prints: int[const(char)[]]

Honesty, key type should be qualified with immutable. Currently
int[const(char[])] can accept char[] key when storing value in the AA, but it's
a known issue.

Anyway in D AA types cannot have mutable key. Therefore this issue should be
marked as invalid.(In reply to Denis Shelomovskij from comment #0)
> This code should compile:
> ---
> void main()
> {
>     int[char[]] aa;
>     aa[new char[1]] = 5; // line 4
> }
> ---
> main.d(4): Error: associative arrays can only be assigned values with
> immutable keys, not char[]
> ---
> 
> Also the error message is wrong. The compiler expects an array of
> not-mutable elements (yes, `cast(const)` will work). This incorrect compiler
> hack [1] was introduced trying to fix Issue 2954 (see Comment 8 of that
> issue). I propose to remove the hack.
> 
> And yes, it's a regression from 2010. )
> 
> 
> [1] http://www.dsource.org/projects/dmd/changeset/749

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