Is there such a thing as a constant instance variable in Ruby?

Question

My googlefu sucks and was unable to find information on this.

Basically I want to have a instance variable that is visible only within the scope of a class/module but is also immutable.

I am new to Ruby and apologize if this question doesn't make much sense.

score 3 · Answer 1 · answered Aug 02 '10 at 23:27

class MyClass
  def initialize
    class << self
      FOO=1
    end
  end
  def foo
    class << self
      FOO
    end
  end
end

Naturally, you'll want to use the method foo wherever possible to read the value.

A simpler equivalent would be

class MyClass
  def initialize
    def foo; 1; end
  end
end

score 1 · Answer 2 · edited May 23 '17 at 11:51

1

Ruby constants aren't very constant: they're not immutable, and you can assign another value to them and all you get is a warning. See the question Constant Assigment Bug in Ruby?

edited May 23 '17 at 11:51

Community

1
1

answered Aug 02 '10 at 23:52

Andrew Grimm

78,473
57
200
338

score 0 · Answer 3 · answered Apr 13 '12 at 05:08

0

I wrote a gem for this case. http://rubygems.org/gems/instancevalue

(The approaching as Ken's one.)

answered Apr 13 '12 at 05:08

kachick

371
2
7

Is there such a thing as a constant instance variable in Ruby?

3 Answers3