3. Calling Scope
c1
@flavor = ‘choc’
@calories = 100
Cookie
flavor=()
flavor ()
Class
- new()
Snack
calories=()
calories()
Module
Object
BasicObject
class Snack
def initialize
@calories = 100
end
end
class Cookie < Snack
def initialize
@flavor = „choc‟
end
end
c1 = Cookie.new
c1.calories looks in this
hierarchy.
Cookie.new looks in
this hierarchy.
For obj.method Ruby will look
in the hierarchy pointed to by
obj’s class.
For method Ruby will look in the
hierarchy pointed to by self’s
class
For @attribute Ruby will look
for the attribute in self.
4. Singletons
c1 Class
Define methods on a specific object that will be
available to only that object and no other object.
Not the same as the singleton creation design pattern!
This is done by “inserting” an anonymous class at the
end of the object’s class hierarchy.
Note, the picture below does not show the usual
Module, Object, BasicObject, etc.
class Cookie
# same as before
end
c1 = Cookie.new
def c1.eat
puts “chomp..chomp”
end
c2 = Cookie.new
c1.eat # => “chomp..chomp”
c2.eat # => no method found
Anon
-eat()
Cookie
Snack
5. Class Methods
c1
Class
Known as “static methods” in C#.
Simply a special case of singletons described in the
previous slide.
An anonymous class is inserted at the end of Cookie’s
class hierarchy.
Anon
-sweet?()
Cookie
Snack
class Cookie
# same as before
def Cookie.sweet?
true
end
end
puts Cookie.sweet?
6. class Cookie
# same as before
end
c1 = Cookie.new
def c1.eat
puts “chomp..chomp”
end
class << c1
def munch
puts “yummy!”
end
end
c1.eat
c1.munch
Another way to define singletons
Singletons
class Cookie
# same as before
def Cookie.sweet?
true
end
class << self
def savory?
false
end
end
end
puts Cookie.sweet?
puts Cookie.savory?
7. extend object with Module
c1 Class
Instance methods of the module are available as
instance methods of that specific object.
Like singleton methods, except loosely coupled.
Anon class points to the Module’s method table
instead of having the methods itself.
Done by “including” the module in a newly created
singleton class.
Anon
Cookie
Snack
module Recipe
def slice
::
end
end
class Cookie < Snack
# same as before
End
c1 = Cookie.new
c1.extend Recipe
c1.slice
Recipe
-slice
methods
8. extend class with Module
c1
Instance methods of the module are available as
class methods of the class.
Like class methods, except loosely coupled.
Cookie
Snack
module Recipe
def slice
::
end
end
class Cookie
extend Recipe
end
Cookie.slice
Anon
Recipe
-slice
methods
Class
9. include Module in class
c1 Class
Instance methods of the module are available as
instance methods of the class.
Like OO inheritance, except loosely coupled.
Done by “inserting” an anonymous class in the middle
of the object’s class hierarchy.
Cookie
Snack
Anon
Recipe
-slice
methods
module Recipe
def slice
::
end
end
class Cookie < Snack
include Recipe
# same as before
End
c1 = Cookie.new
c1.slice
c1.flavor
