Metaprogramming in Ruby: class_eval vs. instance_eval

[beatTheDevil]

I'm using Ruby 1.8.6 btw.

For the longest time today (it seems) I've been trying to understand exactly the operating difference between class_eval and instance_eval. There are some obvious differences I'm perfectly aware of (e.g. class_eval is only on Class objects), but the reality is that some irb tinkering has left me more confused than ever. Given the following:

class Foo
  # could be any class
end
 
f = Foo.new
 
# Try out instance eval on f's class (Foo)
f.class.instance_eval do
  define_method :made_by_inst_eval do
    puts "This method was made by calling instance_eval"
    puts "Current 'self': #{self}"
    puts "Current class of 'self': #{self.class}"
  end
end
 
f.made_by_inst_eval
 

Gives me this:

This method was made by calling instance_eval
Current 'self': #<Foo:0x8f098>
Current class of 'self': Foo

If I then try doing the exact same thing with class_eval instead:

f.class.class_eval do
  define_method :made_with_class_eval do
    puts "This method was made by calling class_eval"
    puts "Current 'self': #{self}"
    puts "Current class of 'self': #{self.class}"
  end
end
 
f.made_with_class_eval
 

I then get the same damn result:

This method was made by calling class_eval
Current 'self': #<Foo:0x8ec88>
Current class of 'self': Foo
 

So, what's the difference between these two calls? In this particular situation? In general?

Some clear thoughts would be ever so appreciated!

[improvcornartist]

There may not be much of a difference in this situation, since both times it is being called on f.class. I think the difference between the two is the receiver of where the method is defined, and thus what it applies to. This page may provide a little extra info around example 5.