Self in method name

Ruby
1

Is there any difference between using self in a method name, and not
using it?
For example, I’ve seen a lot something like

class Foo
def self.bar
…
end
end

Is this the same thing as

class Foo
def bar
…
end
end
?

2

iskaldur wrote:

Is this the same thing as

class Foo
def bar
…
end
end
?

I believe the first is equivalent to:

class Foo
def Foo.bar
…
end
end

and so quite different to the second.

3

The first one creates a class method as opposed to the second one that
creates an instance method (e.g., Foo.bar rather than x = Foo.new;
x.bar;). :slight_smile:

–Jeremy

On 6/12/07, iskaldur [email protected] wrote:

Is this the same thing as

–
http://www.jeremymcanally.com/

My free Ruby e-book:
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My blogs:

http://www.rubyinpractice.com/

4

Hi,

Am Dienstag, 12. Jun 2007, 13:19:02 +0900 schrieb iskaldur:

class Foo
def self.bar
…
end
end

Is this the same thing as

class Foo
class <<self
def bar
…
end
end
end

Bertram

5

Hi –

On Tue, 12 Jun 2007, iskaldur wrote:

Is this the same thing as

class Foo
def bar
…
end
end

def self.bar is just a special case of:

def some_object.some_method

i.e., defining a singleton method on an object (a method that exists
only in the method look-up for that particular object, not for other
objects of its class). Actually it’s not even a special case; it’s
just using the current value of self as the object on which to define
the method.

At the top level of a class definition block, self is the class object
– in this case, Foo. A singleton method defined on a class object
(such as Foo.bar) is usually referred to as a class method. In
addition, class methods are special-cased a bit, in comparison with
other singleton methods… but that’s Lesson Two :slight_smile:

David

6

On 6/12/07, Bertram S. [email protected] wrote:

  def bar
      ...
  end
end

end

Yes, except in the second you’re actually opening up the virtual class
to work on it directly whereas in the first example you’re defining
the method using an absolute name.

It’s easy to see this as a pattern though without understanding the
background, which, hopefully, a brief example will rectify:

class << Fixnum
def x; “y”; end
end

puts Fixnum.x # => “y”
puts 10.x # ERROR

Note that you can dig into virtual classes at any time, not just
within the capacity of a class you’re currently defining :slight_smile:

So… when you see class << self within the definition of another
class, then it’s the equivalent of class << ClassName, and merely
using the “self” to provide the current class rather than naming it
explicitly.

Cheers,
Peter C.

7

class Foo
def self.bar
end

def bar
end
end

Arguably, the equivalent in Java is this:

public class Foo {
public static void bar1() {
}

public void bar2() {
}
}

Notice that you can’t use the same method name statically and
as instance method in Java, whereas you can use the same name
for the class method and the instance method in Ruby.

gegroet,
Erik V. - http://www.erikveen.dds.nl/