From: ptkwt@...1.aracnet.com (Phil Tomson)
Date: 2002-02-20T04:17:41+09:00
Subject: Re: Operator overloading and multiple arguments

In article <20020219102349.X4142@atdesk.com>,
Paul Brannan  <paul@atdesk.com> wrote:
>On Tue, Feb 19, 2002 at 05:37:44AM +0900, Phil Tomson wrote:
>> I'm trying to overload the '<=' operator in a class in order to use it for 
>> assignment:
>> 
>> class Blah
>>   def initialize(value=0)
>>     @value = value
>>   end
>> 
>>   def <=(new_val,time=0)
>>     puts "time is: #{time}"
>>     @value = new_val
>>   end
>> end
>> 
>> a = Blah.new
>> a<=5      #prints: time is 0
>> a<=(8,10) #results in parse error, doesn't like the ','
>> 
>> So apparently you can't have more than one argument for an overloaded 
>> operator (it actually kind of makes sense) - is there any way to do this?
>
>Oddly enough,
>
>  a.<= 5
>  a.<= 8,10
>

Interesting. 

>works, but gives me a creepy feeling in my stomach.  Using overloaded
>operators for alternative assignment behavior doesn't seem justifiable.
>Consider the case where I want to store a Blah object in a binary tree,
>and I expect the <= operator to be available for comparing two Blah
>objects; what will happen then?

Yes, I understand the objection.  But '=' can't be overloaded at all, so I 
wanted to use another symbol.  Also, what I'm doing is creating what I 
call RHDL (Ruby Hardware Description Language) and I wanted it to look as 
much as possible like VHDL which uses '<=' for 'assignment' (it's not 
really assignment, but it'd take too long to get into that).

Anyway, I think it won't be a problem using '<=' for assignment in this 
case.  Here's why:

RHDL has Signal objects which contain Bit objects (A Signal has-a Bit).  
The Bit object carries the value of the signal so comparisons would be 
done in the Bit class and '<=' would mean the normal "less-than-or-equal" 
there.  However at the Signal level, I'll have to define some kind of 
'lte' method. [Of course the obvious question is: Why not just do 
everything at the Bit level and do away with Signal altogether? - Because 
there could be other types of value objects which a Signal could have 
which would behave differently.  Right now there's only Bit, but there 
could be Bit_vector, integers, or some  kindof multi-valued logic system.]

Phil