Just for the sake of learning more about the Ruby object model, I’ve
been doing some experiments, and the following behavior surprised me:
Let’s say we have a class Test:
class Test;end
Then, we class_eval Test.class in order to add a method to the Test
object:
Test.class.class_eval do
def foo
puts ‘foo called!’
end
end
(equivalent to calling Test.class.send(:define_method,:foo) … )
Then:
irb(main):076:0> Test.foo
=> foo called!
But sending foo to class also works:
irb(main):006:0> Test.class.foo
=> foo called!
I still can’t figure out why, though. The Class’ singleton_class doesn’t
contain it (the only possible explanation that came to my mind was that
somehow the method was added to the Class’ singleton class):
Test.class.singleton_methods
=> [:nesting, :constants]
How does the method lookup work in this case? Why does sending :foo to
Test.class also calls the method ? Am I missing something ?
As a reference, I did the same thing with an instance of Test:
irb(main):001:0> class Test;end
=> nil
irb(main):002:0> _foo = Test.new
=> #Test:0x007fa2c39e2f38
irb(main):003:0> _foo.class.class_eval do
irb(main):004:1* def foo
irb(main):005:2> puts ‘foo called!’
irb(main):006:2> end
irb(main):007:1> end
=> :foo
irb(main):008:0> _foo.foo
foo called!
=> nil
irb(main):009:0> _foo.class.foo
NoMethodError: undefined method `foo’ for Test:Class
This worked the way I expected it to.
Thanks in advance!
