Everything is Object 一切皆对象

a = "hello"
a.class # => String

b = 3.14
b.class # => Float

c = %w[pear cat horse]
c.class # => Array

Instance Method & Instance Attribute 实例方法，实例属性

1. Instance Method: 实例方法，成员方法，成员函数
2. Instance Attribute: 实例变量，成员属性，属性(property)，使用@定义

# class

class User

  def initialize name, age
    @name = name
    @age = age
  end

  # getter
  def name
    @name
  end

  def age
    @age
  end

end

user = User.new('Hello', 18)
puts user.name
puts user.age

# class

class User

  def initialize name, age
    @name = name
    @age = age
  end

  # getter
  def name
    @name
  end

  def age
    @age
  end

  # setter
  def name= name
    @name = name
  end

  def age= age
    @age = age
  end


end


user = User.new('Hello', 18)
puts user.name
puts user.age

puts '-' * 30
user.name = 'hello 2'
user.age = 20
puts user.name
puts user.age

# class, attr_reader, attr_writer

class User

  attr_reader :name
  attr_reader :age

  attr_writer :name
  attr_writer :age

  def initialize name, age
    @name = name
    @age = age
  end

end

user = User.new('Hello', 18)
puts user.name
puts user.age

puts '-' * 30
user.name = 'hello 2'
user.age = 20
puts user.name
puts user.age

# class, method

class User

  attr_accessor :name
  attr_accessor :age

  def initialize name, age
    @name = name
    @age = age
  end

  def say_hi
    puts "hello  #{@name}, i am #{@age}"
  end
end

user = User.new('Hello', 18)
user.say_hi

Class Method & Class Variable 类方法，类变量

1. Class Method:类方法，静态方法
2. Class Variable:类变量, 使用@@定义

# class, method

class User

  attr_accessor :name
  attr_accessor :age

  @@counter = 0

  def initialize name, age
    @name = name
    @age = age
    @@counter += 1
  end

  def say_hi
    puts "hello  #{@name}, i am #{@age}"
  end

  def self.get_counter
    @@counter
  end

end

puts User.get_counter
user = User.new('Hello', 18)
user.say_hi
puts User.get_counter

Access Control 访问控制

1. public
2. protected
3. private

# class, method

class User

  attr_accessor :name
  attr_accessor :age

  def initialize name, age
    @name = name
    @age = age
  end


  def say_hello
    puts "hello..."
    say_hi
    say_hey
  end

  def say_hi
    puts "hello  #{@name}, i am #{@age}"
  end

  def say_hey
    puts "hey, i am #{@name}"
  end

  protected :say_hi, :say_hey
end

user = User.new('Hello', 18)
user.say_hello

Dynamic Ruby 动态特性

User内幕

# attr_accessor 方法从哪里来的？
class User
  # ...
end

User.class # => class

# Class.attr_accessor 背后的秘密

# define_method

# attr_accessor, define_method

define_method :hello do
  puts "hello world"
end

hello

自己实现 attr_accessor

# define_method

class User
  # attr_accessor :name
  # attr_accessor :age

  def self.setup_accessor var
    define_method var do
      instance_variable_get "@#{var}"
    end

    define_method "#{var}=" do |value|
      instance_variable_set "@#{var}", value
    end
  end
  
  setup_accessor :name
  setup_accessor :age

  def initialize name,age
    @name = name
    @age = age
  end
end


user = User.new "hello", 18
puts user.name

puts '-' * 30
user.name = "hello 2"
puts user.name