#4625 class_inheritable_accessor should let subclasses inherit from the superclass's attribute - Ruby on Rails

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#4625 ✓resolved

class_inheritable_accessor should let subclasses inherit from the superclass's attribute

Reported by Thomas LECAVELIER | May 17th, 2010 @ 12:31 PM

First a normal case, where things behave as expected:

class A
  class_inheritable_accessor :foo
end

A.foo = 'foo'

class B < A
end

B.foo # => 'foo', as expected

Now, a rather disturbing scenario:

class A
  class_inheritable_accessor :foo
end

class B < A
end

A.foo = 'foo'
B.foo # => nil, 'foo' expected

Should we consider that a bug?

Comments and changes to this ticket

Neeraj Singh May 17th, 2010 @ 03:33 PM

Tag set to “activesupport, patch, rails3”

This is expected behavior. I found following test.

  def test_inheritance
    @klass.class_inheritable_accessor :a
    @klass.a = 'a'

    @sub = eval("class FlogMe < @klass; end; FlogMe")

    @klass.class_inheritable_accessor :b

    assert_respond_to @sub, :a
    assert_respond_to @sub, :b
    assert_equal @klass.a, @sub.a
    assert_equal @klass.b, @sub.b
    assert_equal 'a', @sub.a
    assert_nil @sub.b

    @klass.b = 'b'
    assert_not_equal @klass.b, @sub.b
    assert_equal 'b', @klass.b
    assert_nil @sub.b

    @sub.a = 'A'
    assert_not_equal @klass.a, @sub.a
    assert_equal 'a', @klass.a
    assert_equal 'A', @sub.a

    @sub.b = 'B'
    assert_not_equal @klass.b, @sub.b
    assert_equal 'b', @klass.b
    assert_equal 'B', @sub.b
  end

As you can see

@klass.b = 'b'
assert_not_equal @klass.b, @sub.b

I am adding two lines to the doc to make it clear that child copies attributes from parents when subclass is created.

4625_doc_rails_edge.diff 1.4 KB

Neeraj Singh May 19th, 2010 @ 06:31 AM
This ticket can be closed. I have update the doc.
Rizwan Reza May 19th, 2010 @ 12:19 PM
- no changes were found...
Rizwan Reza May 19th, 2010 @ 12:28 PM
- State changed from “new” to “resolved”
You flagged this item as spam.
Thomas LECAVELIER May 31st, 2010 @ 09:57 AM
- Assigned user set to “Rizwan Reza”
Thanks for your documentation update. It states very clearly the implementation rationale.

However, I believe that implementation violates the Principle of Least Surprise, and that the behavior, despite being documented and tested, is not expected.

What do you think?