From: Pat Maddox <pergesu@...>
Date: 2006-05-14T15:42:47+09:00
Subject: Re: Making sense of the various Ruby "eval"s

I genuinely have no clue what the difference is between class_eval and
instance_eval.  Check out this quick irb session:

irb(main):111:0> class Foo; end
=> nil
irb(main):112:0> Foo.instance_eval { define_method(:foo) { "foo" } }
=> #<Proc:0x00318b00@(irb):112>
irb(main):113:0> Foo.foo
NoMethodError: undefined method `foo' for Foo:Class
        from (irb):113
        from :0
irb(main):114:0> Foo.new.foo
=> "foo"
irb(main):115:0> class Bar; end
=> nil
irb(main):116:0> Bar.class_eval { define_method(:bar) { "bar" } }
=> #<Proc:0x003078a0@(irb):116>
irb(main):117:0> Bar.bar
NoMethodError: undefined method `bar' for Bar:Class
        from (irb):117
        from :0
irb(main):118:0> Bar.new.bar
=> "bar"

I would think that since I used class_eval in one and instance_eval in
the other, SOMETHING should be different..

Pat