play with class inheritance in ruby_Ruby_编程开发_程序员俱乐部

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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.

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

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how to use it?

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w = Word.new

w.palindrome?("foobar") ? => false

w.palindrome?("level") ? ?=> true

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

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class Word < String

def palindrome?

self == self.reverse

end

end

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how to use it?

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s = Word.new("level")

s.palindrome? ? => true

s.length ? => ?5

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inside the Word class, self is the Object itself.

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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.

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

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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.

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

Rails add "blank" method to Object class:

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"".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.

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4. let define a User class this time:

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

end

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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

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

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then in the console:

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require './example_user'
example = User.new
example.name = "Example User"
example.email = "user@example.com"
example.formatted_email

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

so we can create another user by this way:

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user = User.new(:name => "abcd", :email => "abcd@abcd.com")

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It is very common to use hash argument in Rails.

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