[Python-Dev] Global name lookup schemes

[Ka-Ping Yee]

Okay, i spent another afternoon drawing silly pictures full
of boxes and arrows.  I swear, i'm going to be seeing pointers
in my dreams tonight.

Here are figures representing my current understanding of the
various schemes on the table:

    Jeremy 1: the dlict scheme
        http://lfw.org/python/jeremy1.gif
        http://lfw.org/python/jeremy1.tif
        http://lfw.org/python/jeremy1.ai

        Jeremy, i think i'm still somewhat unclear -- notice the
        two question marks in the figure.  What kind of animal
        is the cache?  I assumed that the invalidation info lives
        in an array parallel to the dlict's array.  Is this right?

    Guido 1: the original cellptr/objptr scheme
        http://lfw.org/python/guido1.gif
        http://lfw.org/python/guido1.tif
        http://lfw.org/python/guido1.ai

    Ping 1: guido1 + a tweak to always use two dereferencing steps
        http://lfw.org/python/ping1.gif
        http://lfw.org/python/ping1.tif
        http://lfw.org/python/ping1.ai

    Tim 1: timdicts and cells with shadow flags
        http://lfw.org/python/tim1.gif
        http://lfw.org/python/tim1.tif
        http://lfw.org/python/tim1.ai

GIFs are small versions, TIFs are big versions, AIs are
Adobe Illustrator source files.

Please examine, send me corrections, discuss, enjoy... :)


Still to do:

    Guido 2: the globals_vector scheme

    Skip 1: the global-tracking scheme
        (I don't actually know yet what in this diagram
        would be different from the way things work today.
        Statically, Skip's picture is mostly the same;
        it's the runtime behaviour that's different.
        Still, it's probably good to have a reference
        picture of today's data structures anyway.)


-- ?!ng