From: pjb@... (Pascal J. Bourguignon)
Date: 2009-02-11T18:48:55+09:00
Subject: Re: how to do the recursion

Li Chen <chen_li3@yahoo.com> writes:

> William James wrote:
>
>> def dec_to_binary num, result = []
>>   result <<
>>     if num.odd?
>>       1
>>     else
>>       0
>>     end
>>   if num < 2
>>     result.reverse.join ""
>>   else
>>     dec_to_binary num/2, result
>>   end
>> end
>> 
>> 
>> p dec_to_binary 254
>
>
> Hi Will,
>
> I have one more question about the method call:
>
> When you define method dec_to_binary, you pass two parameters.
> But when you call the method, you only provide one parameter.
>
> Surprisingly Ruby doesn't complain it. How to explain this seemly 
> inconsistancy?

That's possible because we specified a default value of some of these parameters.
William specified an empty array as the default for result:  result = []
I specified an empty string:                                 result=""
That renders the corresponding argument optional.

(Of course, all the parameters with defaults must be last in the
paramater list, and the optional arguments are assigned in order).

-- 
__Pascal Bourguignon__