http://d.puremagic.com/issues/show_bug.cgi?id=8737

           Summary: Associative Array (AA) KeyType is not Unqual-able
           Product: D
           Version: unspecified
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: major
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: monarchdodra@gmail.com


--- Comment #0 from monarchdodra@gmail.com 2012-09-29 15:42:26 PDT ---
There is an issue with AA's, where it is not possible to extract the exact "mutable KeyType" of an AA. This is a built in protection for when iterating on reference keys.

The problem is that it becomes impossible to create new keys, without knowing the "real" type.

This was revealed in a bug in conv.to : #8705 http://d.puremagic.com/issues/show_bug.cgi?id=8705

Reduced test:

--------
import std.stdio;
import std.traits;
import std.conv;

void main()
{
    alias short[short[short]] S;
    alias int[int[int]] T;
    S value;
    T result;

    alias Unqual!(KeyType!T)   K2; // const(int)[int]
    alias Unqual!(ValueType!T) V2; // int

    foreach (k1, v1; value)
    {
        K2 k2 = to2!K2(k1); //request a cast to "const(int)[int]" !!!
        V2 v2 = to!V2(v1);
        result[k2] = v2;
    }
}

T to2(T, S)(S value) //T is const(int)[int]
{
    alias Unqual!(KeyType!T)   K2;
    alias Unqual!(ValueType!T) V2;
    Unqual!T result;

    foreach (k1, v1; value)
    {
        K2 k2 = to!K2(k1); //const(int)
        V2 v2 = to!V2(v1); //int
        result[k2] = v2; //Error: result[k2] isn't mutable (naturally)
    }
    return result;
}
--------
Here, the implementer of "foo" is unable to tranform his keys, because their types are not mutable.

The real problem is that KeyType returned "const(int)[int]", is not really const, but not mutable either. Because of this Unqual doesn't work.

Suggestion: The type returned by KeyType should be "full const", eg:
const(int[int]).

This would make it just as safe, but a user can still request an Unqual on the type.

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--- Comment #1 from monarchdodra@gmail.com 2012-09-29 15:55:11 PDT ---
(In reply to comment #0)
> Here, the implementer of "foo" is unable to tranform his keys, because their types are not mutable.

I meant "to"

> The real problem is that KeyType returned "const(int)[int]", is not really const, but not mutable either. Because of this Unqual doesn't work.
> 
> Suggestion: The type returned by KeyType should be "full const", eg:
> const(int[int]).

No, wait that is bad advice. Recommend changing "Unqual" actually;

--------
template Unqual(T)
    if(!isAssociativeArray!T) //New condition
{
    //As it was
}

//New overload
template Unqual(T)
    if(isAssociativeArray!T)
{
    alias KeyType!T K;
    alias Unqual!(ValueType!T) V;
    alias V[K] Unqual;
}
--------

I'll do this tommorrow, unless I get some objections?

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--- Comment #2 from github-bugzilla@puremagic.com 2012-10-04 11:56:29 PDT ---
Commits pushed to master at https://github.com/D-Programming-Language/phobos

https://github.com/D-Programming-Language/phobos/commit/dabb0343ba173912c8d15ed8cffeedf20420b7f0 fix issue 8737 Unqual for AA

https://github.com/D-Programming-Language/phobos/commit/4bd36016e2385292a86d1acc629d04e939fbf03d Merge pull request #822 from monarchdodra/unqual

fix issue 8737 Unqual for AA

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monarchdodra@gmail.com changed:

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


--- Comment #3 from monarchdodra@gmail.com 2012-10-05 15:39:43 PDT ---
Invalid per https://github.com/D-Programming-Language/phobos/pull/822 .

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