Various issues with get_class interface

[pmichaud]

The get_class opcode doesn't deal well with finding classes using an array, and there are other inconsistencies. Here are some:

(1) PDD15 is inconsistent about the mechanisms available to identify a class PMC. In various places it says:

• class object, namespace object, key, or string name PMC (isa, line 349)
• classname, namespace, or key PMC (get_attr_keyed, line 655)
• class object or namespace key (setattribute, line 951)
• PMC key or namespace object (get_class, line 1034)
• string PMC, namespace key, class object (new, line 1067)

Notably, nowhere does it allow an array to be used to identify a class, although the code does try to allow it (src/oo.c:188) and we allow namespace lookups via arrays.

Ideally I think we ought to be able to identify a class by any of

(a) class object, (b) NameSpace PMC, (c) Key PMC, (d) String PMC.

(2) Looking up a nonexistent class with a String PMC produces a null PMC (correct), but looking up a nonexistent class with an array produces a "get_string() not implemented in class 'ResizableStringArray'" exception:

    $ cat x.pir
    .sub main
        $P0 = box 'NoSuchClass'
        $P1 = get_class $P0
        $I1 = isnull $P1
        say $I1

        $P0 = split '::', 'NoSuchClass'
        $P1 = get_class $P0
        $I1 = isnull $P1
        say $I1

    .end

    $ ./parrot x.pir
    1
    get_string() not implemented in class 'ResizableStringArray'
    current instr.: 'main' pc 15 (x.pir:8)
    $

(2) Even when using an array that does support get_string(), we end up looking up the wrong class:

    $ cat y.pir
    .sub main
        $P99 = newclass '3'

        $P1 = new 'ResizablePMCArray'
        push $P1, 'A'
        push $P1, 'B'
        push $P1, 'C'
        $P0 = get_class $P1    # get class ['A';'B';'C']
        $I0 = isnull $P0
        say $I0

        # what class did we get?
        say $P0
    .end

    $ ./parrot y.pir
    0
    3
    $

Pm