access class variable in ruby

Question

Why class variable in ruby does not behave like static variable, how can I access it simply by doing Mytest.value, instead of MyTest.new.value?

class MyTest
  @@value=0

  def value
    @@value
  end
end

puts MyTest.new.value

It is best to not use class variables. I've completely removed them from my toolkit. Instead, use instance variables on your class, like Erik shows. If your instances also need access to them, give them methods that delegate to the class. — Joshua Cheek
– Joshua Cheek, Commented Jun 9, 2012 at 3:35

Max · Accepted Answer · 2012-06-09 02:47:53Z

7

You want something like

class MyTest
  @@value = 0
  def self.value
    @@value
  end
end

The self makes it a class method, which the class calls directly.

answered Jun 9, 2012 at 2:47

Max

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Comments

Érik Desjardins · Accepted Answer · 2012-06-09 04:16:54Z

2

[EDIT] Read comments to know why not doing this.

class MyTest
  @value=0

  class << self
    attr_accessor :value
  end
end

Instead, if you really need to access variable in such ways, I suggest a simple module.

Otherwise, like Joshua Cheek commented on the original post, you should use Instance Variable for your class and have accessors.

edited Jun 9, 2012 at 4:16

answered Jun 9, 2012 at 2:44

Érik Desjardins

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3 Comments

Max Over a year ago

While this behaves similarly, there are important differences between class variables and instance variables for class objects (the big one being how they are treated by inheritance). Also, class << self is outdated notation. Recent Ruby versions have singleton_class and define_singleton_method methods, which are easier to read.

Érik Desjardins Over a year ago

You are right, the right way of doing this is well, the answer you just posted.

Andrew Marshall Over a year ago

The term "static" doesn't really apply in Ruby.

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