From: Stefano Crocco <stefano.crocco@...>
Date: 2008-04-07T18:11:33+09:00
Subject: Re: Calling class method from instance method

On Monday 07 April 2008, Yu-shan Fung wrote:
> Pretty dumb question -- how do I call a class method from inside an
> instance method (of the same class)?
>
> The use case I have is that in an activerecord model class, I would like
> to define an instance method which calls find_by_sql.
>
> I have tried and found that this works:
>   self.class.find_by_sql
>
>
> But this seems pretty verbose for something so obvious.
>
> Thanks!

You can replace self.class with the name of the class. For example:

class C
  
  def C.x
  end

  def y
    self.class.x
    C.x
  end

end

There's a difference, however. If you derive a class from C and override C.x 
from D:

class D < C
  def self.x
  end
end

using self.class.x from C#y will use the version of x defined in the 
instance's class (that is, C.x if called by an instance of C and D.x if called 
by an instance of D). Using C.x will, obviously, always call C.x. Here's some 
code which demonstrates this:

class C
  def self.x
    puts "x of C"
  end

  def y
    self.class.x
  end

  def z
    C.x
  end
end

class D < C
  def self.x
    puts "x of D"
  end
end

puts "Calling y on an instance of C"
C.new.y
puts "Calling y on an instance of D"
D.new.y
puts "Calling z on an instance of D"
D.new.z

I hope this helps

Stefano