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суббота, 28 декабря 2013 г.
★ ШКОЛЬНЫЙ ПОРТАЛ, Антон Гудман оставил для вас сообщение
четверг, 3 октября 2013 г.
Ruby :: Class Variables and Methods
Class methods do not have access to instance methods or instance
variables. However instance methods can access both class methods and
class variables.
Recall that an instance variable always has an
One of the places where class variables do find proper use is to store application configuration - things like application name, version, database and other settings. The next exercise is to build one such class
class instance variables
Recall that an instance variable always has an
@ symbol prefixed before its name. Similarly, class variables are prefixed with @@.One of the places where class variables do find proper use is to store application configuration - things like application name, version, database and other settings. The next exercise is to build one such class
ApplicationConfiguration. You have to define two class-level methods: set and get.
The set method takes two parameters: property_name and value. The get
method takes one parameter: property_name, and should return the value
that corresponds to the property.class instance variables
class Item
def self.show
puts "Class method show invoked"
end
end
class Item
class << self
def show
puts "Class method show invoked"
end
end
end
Ruby :: Instance Variables and Accessors
class Item
def initialize(description, color)
@description = description
@color = color
end
def description=(new_description)
@description = new_description
end
def color=(new_color)
@color = new_color
end
end
rubymonk.com/learning/books/4-ruby-primer-ascent/chapters/45-more-classes/lessons/110-instance-variables#solution4434
def initialize(description, color)
@description = description
@color = color
end
def description=(new_description)
@description = new_description
end
def color=(new_color)
@color = new_color
end
end
rubymonk.com/learning/books/4-ruby-primer-ascent/chapters/45-more-classes/lessons/110-instance-variables#solution4434
Ruby :: Instance Variables and Accessors :: getter and setter methods
So far we talked about accessing the contents of an instance variable
through getter methods. Now, how do you change the value of the instance
variables from outside? That is where setter methods come into play.
Ruby :: Redefining, overriding, and super
class Item
attr_reader :item_name, :qty
def initialize(item_name, qty)
@item_name = item_name
@qty = qty
end
def to_s
"Item (#{@item_name}, #{@qty})"
end
def ==(other_item)
puts "Method == called on #{self} with parameter #{other_item}"
return self.to_s == other_item.to_s
end
end
p Item.new("abcd",1) == Item.new("abcd",1)
p Item.new("abcd",2) == Item.new("abcd",1)
class Fixnum
def +(other)
42
end
end
Most object oriented languages offer a mechanism by which an overridden method can be called by the overriding method. Ruby uses the
class Animal
def move
"I can move"
end
end
class Bird < Animal
def move
super + " by flying"
end
end
attr_reader :item_name, :qty
def initialize(item_name, qty)
@item_name = item_name
@qty = qty
end
def to_s
"Item (#{@item_name}, #{@qty})"
end
def ==(other_item)
puts "Method == called on #{self} with parameter #{other_item}"
return self.to_s == other_item.to_s
end
end
p Item.new("abcd",1) == Item.new("abcd",1)
p Item.new("abcd",2) == Item.new("abcd",1)
class Fixnum
def +(other)
42
end
end
Most object oriented languages offer a mechanism by which an overridden method can be called by the overriding method. Ruby uses the
super keyword to make this happen. Using super will call the same method, but as defined in the superclass and give you the result.class Animal
def move
"I can move"
end
end
class Bird < Animal
def move
super + " by flying"
end
end
Ruby :: Understanding Inheritance
puts Float.instance_methods.count #201
puts (Float.instance_methods - Object.instance_methods).count #87
puts (Float.instance_methods - Object.instance_methods).count #87
Ruby :: Classification
As you've probably guessed,
Object#is_a? accepts a single parameter - a class. Object#is_a? has an alias, Object#kind_of?.
They're identical in every respect so you're free to pick whichever reads better in a given context.
quick summary
- Classes act as templates for the creation of objects, specifying their state and behaviour
- An object created by a class is called an instance of that class
- A class is itself an object, and an instance of the class
Class
Ruby :: Blocks, Procs, and Lambdas
The
-> literal form is a shorter version of Kernel#lambda.Kernel#proc factory method is identical to Proc.new. Note that proc is a method and not a literal form like -> nor a keyword like yield.воскресенье, 10 февраля 2013 г.
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