From: Robert Klemme <shortcutter@...>
Date: 2011-04-07T20:53:34+09:00
Subject: Re: Hash Surprises with Fixnum, #hash, and #eql?

On Thu, Apr 7, 2011 at 1:20 PM, Phillip Gawlowski
<cmdjackryan@googlemail.com> wrote:
> On Thu, Apr 7, 2011 at 11:19 AM, Robert Klemme
> <shortcutter@googlemail.com> wrote:
>>
>> I also doubt whether it is a good idea to allow for subclassing of an
>> integer like class.  What use case do you have in mind which would
>> make this necessary?
>
> Complex numbers come to mind:

Why bother, it has been done already.

irb(main):006:0> x = Complex(0,-1)
=> (0-1i)
irb(main):007:0> x * x
=> (-1+0i)
irb(main):008:0> (x * x)+0
=> (-1+0i)
irb(main):009:0> (x * x).to_int
=> -1

And they do play nicely as ints - as long as it's possible:

irb(main):011:0> %w{foo bar baz}[x*x]
=> "baz"
irb(main):012:0> %w{foo bar baz}[x]
RangeError: can't convert 0-1i into Integer
        from (irb):12:in `to_i'
        from (irb):12:in `to_int'
        from (irb):12:in `[]'
        from (irb):12
        from /opt/bin/irb19:12:in `<main>'

> 3 - 2j [+|*] 45^(j * e * 44°).
>
> Very different semantics for addition and multiplication of those than
> for your normal space numbers, including conversion from Cartesian to
> polar form. Bit of a textbook case for the benefits of inheritance and
> function overloading. :P
>
> It'd be better to have those be a sub-class of Float, though.

Actually it's Numeric which is correct because not every Complex _is a_ Float!

irb(main):010:0> Complex.ancestors
=> [Complex, Numeric, Comparable, Object, Kernel, BasicObject]

Cheers

robert

-- 
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