ruby - Dose self.class.class_eval equal to instance_eval? -

i want find out difference between instance_eval , class_eval,so did work。after searching internet， figure out something， there comes other question can't understand！when i'm doing this:

class findme    def method_missing method, *args, &block     method = method.to_s     self.class.class_eval <<-eof, __file__, __line__       def #{method}         puts "i'm instance method! i'm #{method}"       end     eof     send method, *args   end    def self.method_missing method, *args, &block     method = method.to_s     instance_eval <<-here, __file__, __line__       def #{method}         puts "i'm class method! i'm #{method}"       end     here     send method, *args   end  end  findme.new.hello findme.hello 

i

i'm instance method! i'm hello i'm class method! i'm hello 

when change code :

class findme    def method_missing method, *args, &block     method = method.to_s     self.class.class_eval <<-eof, __file__, __line__       def #{method}         puts "i'm instance method! i'm #{method}"       end     eof     send method, *args   end    def self.method_missing method, *args, &block     method = method.to_s     self.class.class_eval <<-here, __file__, __line__       def #{method}         puts "i'm class method! i'm #{method}"       end     here     send method, *args   end  end  findme.new.hello findme.hello 

i same output, can 1 tell what's going on?

by class_eval modify class, instance_eval current instance only. look:

▶ class ▷   def ceval ▷     self.class.class_eval "def on_class ; puts 'on class' ; end" ▷   end ▷   def ieval ▷     self.instance_eval "def on_instance ; puts 'on instance' ; end" ▷   end ▷ end ▶ a1 = a.new #⇒ #<a:0xcf6a87c> ▶ a1.ceval #⇒ :on_class ▶ a1.ieval #⇒ :on_instance ▶ a1.on_class #⇒ on class ▶ a1.on_instance #⇒ on instance  ▶ a2 = a.new #⇒ #<a:0xd0e9f7c> ▶ a2.on_class #⇒ on class  !!! defined on newly created instance of ▶ a2.on_instance #⇒ nomethoderror: undefined method `on_instance' #<a:0xd0e9f7c> 

the latter fails because declare on_instance method on instance a1, , a2 knows nothing it.