4.4 play with class inheritance in ruby

 

1. 

class Word
    def palindrome?(string)
        string == string.reverse
    end
end

 in this class, it doesn't indicate superclass explicitly, so the default is inherit from Object class.

 

since it doesn't define initialize method, it will use the initialize method of Object class.

 

how to use it?

 

w = Word.new

w.palindrome?("foobar")   => false

w.palindrome?("level")    => true

 

2. a better definition will be inherit from String class:

 

class Word < String

def palindrome?

self == self.reverse

end

end

 

how to use it?

 

s = Word.new("level")

s.palindrome?   => true

s.length   =>  5

 

inside the Word class, self is the Object itself.

 

3. and next, we find it will be more natural to define the palindrome? method in the String class itself, so that we can call it on a string directly.

 

Ruby will let you do this, Ruby classes can be opened and modified, allowing developer to add methods:

 

 

class String
    def palindrome?
        self == self.reverse
    end
end

 although this feature is very powerful, you need to be careful, 

don't do it unless you have a really good reason.

 

Rails add many methods to ruby for good reasons, for example, 

Rails add "blank" method to Object class:

 

 

"".blank?
=> true
"           ".empty?
=> false
"           ".blank?
=> true

nil.blank?
=> true

 because in web dev, we often want to prevent var from being blank, like space or other whitespace.

 

 

4. let define a User class this time:

 

 

class User
  attr_accessor :name, :email
  
  def initialize(attributes = {})
    @name = attributes[:name]
    @email = attributes[:email]
  end
  
  def formated_email
    "#{@name} <#{@email}>"
  end

end

 

attr_accessor  defines the get and set method for @name and @email.

initialize method is special in Ruby, it is called when exec User.new

 

save this part of code into a file called example_user.rb

 

then in the console:

 

 

require './example_user'
example = User.new
example.name = "Example User"
example.email = "[e-mail]"
example.formatted_email

 

 

 

Remember that we can omit the {} in the final hash param when calling a method.

so we can create another user by this way:

 

 

user = User.new(:name => "abcd", :email => "[e-mail]")

 

It is very common to use hash argument in Rails.