a inherent class, how to write?

[Zhenning Guan]

I have a file like this;

class File
class << self
def diff
#some stuff--------------
end
end
end

def method_1
#-----------
end

def method_2
#------------
end


method_1
method_2
------------------------------------
now ,I need to rewrite this file.

but I don't how to deal with the class File....

one.
+++++++++++++++++++
class File
class << self
def diff
#some stuff--------------
end
end
end

class Myclass
def method_1
end

def method_2
end
end

++++++++++++++++++++

two
++++++++++++++++++++
class Myclass
class File
class << self
def diff
#some stuff--------------
end
end
end

def method_1
end

def method_2
end
end
+++++++++++++++++++++


so, which way should I use?
any thought will be appreciated.

 

[Robert Klemme]

I have a file like this;

class File
class << self
def diff
#some stuff--------------
end
end
end

def method_1
#-----------
end

def method_2
#------------
end


method_1
method_2
------------------------------------
now ,I need to rewrite this file.

but I don't how to deal with the class File....

one.
+++++++++++++++++++
class File
class << self
def diff
#some stuff--------------
end
end
end

class Myclass
def method_1
end

def method_2
end
end

++++++++++++++++++++

two
++++++++++++++++++++
class Myclass
class File
class << self
def diff
#some stuff--------------
end
end
end

def method_1
end

def method_2
end
end
+++++++++++++++++++++

That's difficult to answer since we cannot see how your method_1 and
method_2 use class File.

In the general case inheritance is done like this:

class A
end

class B < A
end

B is now subclass of A.

Kind regards

robert

 

[David A. Black]

Hi --

How is that different from
class File
def diff
#some stuff--------------
end
end
?

Still learning...

The construct:

class << object
# ...
end

puts you into a class definition block for the singleton class of
object. The singleton class is where the methods are defined that are
specific to that exact object (as opposed to those that the object
gets from its class).

In this case:

class File
class << self

"self" is the class object File (because when you're in a class
definition block, "self" is set to the class object). The methods
defined in the inner definition block will be callable only directly
on File itself (and its subclasses; classes get to share their
singleton methods with their subclasses)[1]. So you'll be able to do:

File.diff

but not

f = File.new(...)
f.diff # wrong; it's not an instance method

If you do

class File
def diff

then you're defining an instance method.

For more info, see http://www.wobblini.net/singletons.html. (And for a
lot more info, see http://www.manning.com/black2


David

[1] And singleton methods of class objects are more commonly referred
to as "class methods".

--
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.rubypal.com
Now available: The Well-Grounded Rubyist (http://manning.com/black2)
Training! Intro to Ruby, with Black & Kastner, September 14-17
(More info: http://rubyurl.com/vmzN)