class inheritance

Robert Kern robert.kern at gmail.com
Tue Mar 16 16:06:10 CET 2010


On 2010-03-16 07:35 AM, Dave Angel wrote:
>
>
> Carl Banks wrote:
>> On Mar 15, 4:34 pm, JLundell <jlund... at pobox.com> wrote:
>>> It's also unfortunate that Python doesn't have an approximately-equal
>>> operator; it'd come in handy for floating-point applications while
>>> preserving hash. If only there were a ~=r ≈ operator I could
>>> overload. And ~ is unary, so no joy.
>>
>> One problem with it is that there's no way to make it universal;
>> different appiplications have different ideas of close. Conceivably
>> it could be usefully defined for a user type though..
>>
>> Bacause of this problem almost no languages have an almost equal
>> operator. I'm curious what languages do, of if there are any with a
>> trinary operator that also takes a threshold.
>>
>> Carl Banks
>>
> If I recall correctly, APL has a *fuzz* value, which is used in all(?)
> comparisons. But I do not recall anything about how it was defined. I do
> recall that you could change the threshold, and suspect it was relative
> to the operands. For symmetry, it would probably have to be relative to
> the average of the two values, or some such.

The problem is that frequently there is no system-wide fuzz value which is 
appropriate for all comparisons in a given program. You need to choose the right 
value for each comparison. Consequently, you might as well use a function 
instead of an operator and a global variable.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco




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