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Date: Sun, 19 May 2013 11:54:04 +1000
From: Cameron Simpson <cs@zip.com.au>
To: Chris Angelico <rosuav@gmail.com>
Subject: Re: mutable ints: I think I have painted myself into a corner
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On 19May2013 11:11, Chris Angelico <rosuav@gmail.com> wrote:
| On Sun, May 19, 2013 at 10:26 AM, Cameron Simpson <cs@zip.com.au> wrote:
| > Before I toss this approach and retreat to my former "object"
| > technique, does anyone see a way forward to modify an int subclass
| > instance in place? (That doesn't break math, preferably; I don't
| > do arithmetic with these things but they are, after all, ints...)
| 
| Why is it an int subclass? Because there are places where you want to
| use it as though it were an int? It might be easier to render those,
| instead, eg by creating a __int__ method. (Or is it "an __int__
| method"? Not sure.)

I don't want to use it as an int, on the outside. I want to use an
int on the inside as the implementation.

It's an int _subclass_ so that it is no bigger than an int. Otherwise
I may as well just make an ordinary object and be back where I
started.  Bulky:-(

The reason it is an _int_ subclass, versus something else, is that
a bitmap is a type of int. So the functional mapping is direct.

I _do_ _not_ want to operate on it from the outside as an int (doing
overt addition, for example, though I can imagine doing bitwise
activities); I want to operate on in _internally_ as a int to decide
what names-by-an-attribute flags are on or off.

So an object with an __int__() method is right out; it's the wrong
interface because it would mean an int() call (possibly implicit)
in exterior code.

Cheers,
-- 
Cameron Simpson <cs@zip.com.au>

Hoping to shave precious seconds off the time it would take me to get
through the checkout process and on my way home, I opted for the express
line ("9 Items Or Less [sic]"  Why nine items?  Where do they come up with
these rules, anyway?  It's the same way at most stores -- always some
oddball number like that, instead of a more understandable multiple of
five.  Like "five.")
        - Geoff Miller, geoffm@purplehaze.Corp.Sun.COM