From: zdennis <zdennis@...>
Date: 2006-01-16T22:29:51+09:00
Subject: Re: basic question about Fixnum & Integer

Tom Allison wrote:
> Hello,
> I'm really new to Ruby and rather new to OOP in general.  I've been 
> using Perl for about 7 years now and have a fairly good understanding of 
> that language.  I've never really entertained Python to any serious 
> degree beyond 'Hello World'.  Now you know my background.
> 
> I tried to do the following:
> 
> 13.lcd 3
> 
> and it failed in the irb.
> 
> Why?
> 
> My thinking is that 13 is a Fixnum class and Fixnum inherits Integer.
> Integer has a method 'lcd' that returns the least common denominator.
> Since Fixnum < Integer then all the methods of Integer should be 
> available to all the child objects (Fixnum and super).  And if this is 
> true, then calling a method like I did (Fixnum#lcd) implies an 
> inheritance search to find that class.
> 
> But my thinking seems to not reflect Ruby very well.
> 
> Can someone please tell me what I did wrong in the code and also in 
> thought?  It's little niggly bits like this that get frustrating.
> 

Hi Tom,

There is no method named "lcd" on Integer, unless perhaps you're using an outside library which 
gives you this functionality.

irb(main):016:0> 5.respond_to? :lcd
=> false


To check what methods an Integer does have you can use the public_methods method on any number.

irb(main):017:0> 5.public_methods.sort
=> ["%", "&", "*", "**", "+", "+@", "-", "-@", "/", "<", "<<", "<=", "<=>", "==", "===", "=~", ">", 
">=", ">>", "[]", "^", "__id__", "__send__", "abs", "between?", "ceil", "chr", "class", "clone", 
"coerce", "display", "div", "divmod", "downto", "dup", "eql?", "equal?", "extend", "floor", 
"freeze", "frozen?", "hash", "id", "id2name", "inspect", "instance_eval", "instance_of?", 
"instance_variable_get", "instance_variable_set", "instance_variables", "integer?", "is_a?", 
"kind_of?", "method", "methods", "modulo", "next", "nil?", "nonzero?", "object_id", "prec", 
"prec_f", "prec_i", "private_methods", "protected_methods", "public_methods", "quo", "remainder", 
"respond_to?", "round", "send", "singleton_method_added", "singleton_methods", "size", "step", 
"succ", "taint", "tainted?", "times", "to_a", "to_f", "to_i", "to_int", "to_s", "to_sym", 
"truncate", "type", "untaint", "upto", "zero?", "|", "~"]

You can also check ruby-doc for method documentation online, http://www.ruby-doc.org/


Zach