From: Gary Wright <gwtmp01@...>
Date: 2008-02-20T08:37:22+09:00
Subject: Re: Is there any object-oriented File class in ruby ?


On Feb 19, 2008, at 5:45 PM, tom_33 wrote:
> Now my question is what have I been missing here ?
> I mean, is there any other much better File class somewhere in the
> Ruby core that is more pure OO, or otherwise why is a language with a
> CORE procedural "class" library described as being a pure oo
> language ?

It is described as 'pure' because almost all actions are a side- 
effect of sending a message to an object. In your example

    File.basename('/dir/file')

File is the object, basename is the message, and '/dir/file' is an  
argument (an instance of String). The most obvious example of the  
pervasiveness of this pattern is methods on integers:

    3.next            # 4
    3.to_s(2)         # "11", 3 as a string of binary digits
    (-3).abs          # 3 the absolute value of -3
    (3.1415).floor    # float value rounded down to integer

Many static syntactical constructs also have a dynamic/method based  
interface:

# subclass A statically

class A < B
   def foo
     42
   end
end

# subclass A dynamically

class_b = Class.new(A) {
   def foo
     42
   end
}

A big milestone in learning Ruby is to fully understand what it means  
for a class to be an object at runtime. With regard to the methods  
you were looking at. If you think of File as an object representing  
the file system then:

   File.basename(path)  # file system parses path
   File.open(path)      # file system looks up path and returns file  
instance

There is also Pathname, a class for manipulating file path strings  
and looking up file properties. It provides a unifying interface to  
other classes such as File, Dir, FileTests, String, and so on.

path = Pathname.new("/etc")
path.directory?               # consults filesystem to see if "/etc"  
is a directory
path.atime                    # consutls filesystem to get atime of "/ 
etc"

It is also important to realize that Ruby is a practical language in  
that there is often more than one way to skin a cat with Ruby as  
opposed to a 'one correct way'.  So you can muck around with strings  
and regular expressions to parse path names or use File or use  
Pathname or roll your own class.

Gary Wright