From: ptkwt@... (Phil Tomson)
Date: 2004-04-09T14:24:16+09:00
Subject: Would a ':=' operator break anything?


This is from something that came up in another thread.

Someone wanted to be able to overload the '=' operator.  There was a time 
a few year back when I wanted to be able to do this as well, but now I 
agree it is ill-advised and would endanger global peace (0ops, too late). 
;-)

Would allowing for overloading a ':=' operator break anything? (seems kind 
of Pascalish :)

Why would you want to do this?

I've got a class like so:

class Ternary #can only take on values 0,1,2
  def initialize(value=0)
    check_value(value)
    @value = value
  end

  def check_value(value)
    if value > 3 || value < 0
      raise OutOfRangeException, "value is out of range"
    end
  end

  def :=(value)  #not currently possible, but it would be cool
    check_value(value)
    @value = value
  end

  def +(value)
    Ternary.new((@value + value)%3)
  end

  def -(value)
    Ternary.new((@value - value)%3)
  end

end

This would allow you to do:

  b = Ternary.new
  b := 2
  b := 42 #raise exception

So the ':=' operator 'looks' close enough to assignment so that the 
meaning is clear and it keeps me from having to do:

  b.assign 42

Which is how I do it currently with this class and several other classes 
I've come up with over the years.

So how about it, would allowing a ':=' operator break anything?

I would tend to think not as the ':' appears either as '::' or :symbol so 
there shouldn't be a case where ':' and '=' can legally appear together 
now (but I could be overlooking something).

Phil