Ruby object model

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Chhorn Chamnap
Yoolk Mango
4 Aug 2010

 Basic Ruby
 Methods
 Classes
 Method-Access Rules
 What’s in an Object?
 Classes in Depth
 What Happ...

 Local variables
 start with a lowercase letter or an underscore
Eg: x, string, __abc__, start_value, and fi...

 Class variables
 store information per class hierarchy
 follow the same rules as instance variables
 st...

 predefined, reserved terms associated with
specific programming tasks and contexts.
 def,
 class,
 ...

 Ruby interprets it as one of three things:
 A local variable
 A keyword
 A method call
 Here’s how R...

 When you load a file, Ruby looks for it in each of its
load path.
 The last directory is the current directory.
 loa...

 Doesn’t reload files if already loaded.
 require "loadee"
 require "/home/users/code/loadee"

 Follow the same rules and conventions as
local variables
 except, can end with ?, !, or =
 Methods are exp...

 Ruby sees all data structures and values as
objects.
 x = "100".to_i(9)
 Methods can take arguments.
 P...

 Have to supply the correct number of
arguments.

 A method that allows any number of
arguments.

def multi_args(*x)
puts "I can take zero or more argument...

def default_args(a,b,c=1)
puts "Values of variables: ",a,b,c
end

default_args(3,2)

 Ruby tries to assign values to as many variables
as possible.
 The sponge parameters get the lowest priority.

 Required ones get priority, whether they
occur at the left or at the right of the list.
 All the optional ones ...

 Classes define clusters of behavior or
functionality.
 Classes can respond to messages, just like
objects.
...

 In Ruby, classes are objects.
 The new method is a constructor.
 Classes are named with constants.

 Ruby executed the code within the class just
as it would execute any other code.

 It’s possible to reopen a class and make
additions or changes.

 These methods defined inside a class.
 Used by all instances of the class.
 They don’t belong only to one object.

 Enables individual objects to remember state.
 Always start with @.
 Visible only to the object to which they
...

 Define a special method called initialize.

 Ruby allows you to define methods that end
with an equal sign (=).
def price=(amount) ticket.price=(63.00)
...

 The attributes are implemented as reader
and/or writer methods.

 Ruby supports only single inheritance.
 Classes can import modules as mixins.
 The class Object is almost at the...

• Private methods can’t be called with an explicit receiver.

class Baker class Baker
def bake_c...

 It’s OK to use an explicit receiver for private
setter methods.

 The top-level method is stored as a private
instance method of the Object class.

 Every object is “born” with certain innate
abilities.
 object_id
 respond_to?
 send
 methods
...

 Not uncommon to define a method called
send.
 Then, use __send__ instead.
 public_send, a safe version of se...

 Every class is an instance of a class called
Class.
 You can also create a class the same way you
create mo...

 The class Class is an instance of itself.
 Object is a class, Object is an object.
 And Class is a class. And Ob...

 Classes are objects.
 Instances of classes are objects, too.
 A class object has its own methods, its own
st...

 When you call a method, Ruby does two
things:
 It finds the method (method lookup).
 It executes the met...

 “one step to the right, then up.”

 How objects call their methods?
 From their class
 From the superclass and earlier ancestors of their
...

 The class Class has two new methods as:
 a class method; Class.new
 an instance method; Ticket.new
 Insta...

 Modules are bundles of methods and
constants.
 Modules don’t have instances.
 Consists of the functionality ...

 Modules get mixed in to classes, using the
include method, referred to as mix-ins.
 The instances of the class ...

 To resolve a message into a method:
 Its class
 Modules mixed into its class
 The class’s superclass
...

 Define a method twice inside the same class,
the second definition takes precedence.
class D
def hello
...

 If the object’s method-lookup path includes
more than two same methods, the first one is
the “winner”.

 A class mixes in two or more modules.
 The modules are searched in reverse order of
inclusion

class C
include M
include N
include M
end

 Re-including a module doesn’t do anything.
 N is still considered...

 Use the super keyword to jump up to the
next-highest definition, in the method-
lookup path.

 The way super handles arguments:
 Called with no argument list – super
 Called with an empty argument list –...

 The Kernel module provides an instance method called
method_missing.

 Nested module/class chains are used to
create namespaces for classes, modules, and
methods.
module Tools
...

 Begin with an uppercase letter.
eg: A, String, FirstName, and STDIN
 (FirstName) or (FIRST_NAME) is usual.
 ...

 You get a warning if you reassign to the
constant.

 To modify a constant, use a variable instead.

 not ...

 Constants have a kind
of global visibility or
reachability.
 Bears a close
resemblance to
searching...

 Like /, the :: means “start from the top level.”

 At every moment, only one object is playing
the role of self.
 Self is the default object or current object.
 ...

 But what is self when you haven’t yet entered
any definition block?
 The answer is that Ruby provides you wit...

 In a class or module definition, self is the class
or module object.

 In a method definition, self is the object that
called it.

 When a singleton method is executed, self is
the object that owns the method.

 If the receiver of the message is self, you can
omit the receiver and the dot.

 If both a method and a variable of a given
name exist (talk), the variable takes
precedence.
 To force Ru...

 Every instance variable belongs to self.

 Scope refers to the reach or visibility of
variables and constants.
 Three types of variables: global, local, a...

 Global scope is scope that covers the entire
program.
 Global scope is enjoyed by global variables.

 Local scope is a basic layer of every Ruby
program.
 Every time you cross into a class, module, or
def keyw...

 Provides a storage mechanism shared
between a class and its instances.
 Visible only to a class and its instanc...

 They’re class-hierarchy variables.

 Let’s say we’ve created our Ticket class.
 Ticket isn’t only a class.
 Ticket is also an object in its own r...

 Where do singleton methods live?
 The singleton class
 Every object has two classes:
 The class of which ...

 Singleton classes are anonymous.
 The << object notation means the anonymous,
singleton class of object.

 The Well-Grounded Rubyist, David A. Black
 Metaprogramming Ruby, Paolo Perrotta

Share Slideshare

LinkedIn
Facebook
Twitter

Embed

Size (px)

Show related Slideshows at end

WordPress Shortcode

Link

Share
Email

Advanced Ruby Idioms So Clean You C... by Brian Guthrie 8049 views
The Ruby Object Model by Rafael Magana by Rafael Magana 2460 views
«Работа с базами данных с использов... by Olga Lavrentieva 1444 views
Beginner's Sinatra by Tomokazu Kiyohara 2856 views
ZODB Tips and Tricks by Carlos de la Guardia 3549 views
Magic in ruby by David Lin 1807 views

View on Slideshare

1 of 100 Ad

View on Slideshare

1 of 100 Ad