From: jbshaldane@... (haldane)
Date: 2002-02-14T22:59:04+09:00
Subject: Bitwise operators ability to coerce

This discussion continued from RubyGarden on request of matz...

>I notice that none of the bitwise operators have the ability to coerce - 
>so in my class Foo (which has an attribute @value)... 
>  def initialize(n)
>    @value=n
>  end
>  def coerce (number)
>    [Foo.new(number), self]
>  end
>  def | (n)
>    if n.is_a? Foo
>      @value | n.value
>    else
>      @value | n
>    end
>  end
>..does not work as intended. It looks to me like this ability could 
>easily be added in numeric.c - how about it? 
>haldane.
__
>When you want to define "coerce" method to convert your object to integers, 
>I guess there's better conversion scheme: >to_int. 
>The object that defines "to_int" behave like integers. 
>matz.
__
>Yes, to_int would be ok for my example, but not for what I am really doing 
>- my real-life class does other stuff instead of just returning integers. 
>It seems inconsistent that all the other numeric operations call coerce 
>except for the bitwise ones. 
>There is a work around: to redefine the bitwise operators in class Fixnum 
>and handle it there - but it would be nicer if all the operators worked alike.
>haldane.
__
>Could you be more concrete? Or perhaps we can discuss on the ruby-talk list. 
>Coerce does not have operator information, so that it might not solve your 
>problem either. 
>Bitwise operators do not call coerce because they are integer operation. 
>You can't define bitwise-or between integer and float. 
>matz.
__
What I am doing is generating instructions for another language from my Ruby
code. The other language has integers, and arithmetic operations including
bitwise ones.  So, when I see x.val= y + 2, the + operator causes output of
instructions to add 2 to y and returns an 'immediate' object, which the val= 
method sees and knows to output instructions to take whatever was on the 
stack and assign it to x. I guess it's a cheap way of getting a parser!

So it would be nice to be able to write 3 | x as well as x | 3.  For the other
operators, coerce is an elegant way for me to do this.

I appreciate you don't want to coerce to floats because there are no float 
bitwise ops.

I think the least surprising way for this to work is for Ruby
to test if there is a | (or whichever bitwise op) method for whatever object
it was passed, and to try to coerce if there is one.  What do you think?

haldane.