Evil Eval

dynm.rb

class Person
end

person = Person.new
Person.instance_eval "attr_accessor :name"

person.name = "bobby" 
puts person.name 

person.instance_eval "def greet; puts 'hello ' end"

person.greet

person2 = Person.new

begin
person2.greet
rescue
puts "Yep only object person has this behavior"
end

puts "Type in a method: "
person.instance_eval $stdin.gets.chomp

p person.methods - Object.instance_methods

# Output: 
# bobby
# hello 
# Yep only object person has this behavior
# Type in a method: def methy; 'hello' end
# [:greet, :methy, :name, :name=]