defining_methods.rb

#### these options use the eigenclass ####

## def on an identifier

my_object = Object.new

def my_object.foo
  puts "foo"
end

my_object.foo

## define_singleton_method

my_object = Object.new

my_object.define_singleton_method(:foo) do
  puts "foo"
end

my_object.foo

## def inside the eigenclass

my_object = Object.new

class << my_object
  def foo
    puts "foo"
  end
end

my_object.foo

## define_method on the eigenclass

my_object = Object.new

class << my_object
  define_method(:foo) do
    puts "foo"
  end
end

my_object.foo

## def inside a module we extend

my_module = Module.new do
  def foo
    puts "foo"
  end
end

my_object = Object.new
my_object.extend(my_module)

my_object.foo

## define_method on a module we extend

my_module = Module.new
my_module.define_method(:foo) do
  puts "foo"
end

my_object = Object.new
my_object.extend(my_module)

my_object.foo

#### these options use class ancestry ####

## def inside a class that we inherit from

my_class = Class.new do
  def foo
    puts "foo"
  end
end

my_object = my_class.new

my_object.foo

## define_method on a class that we inherit from

my_class = Class.new
my_class.define_method(:foo) do
  puts "foo"
end

my_object = my_class.new

my_object.foo

#### only `Module` has define_method ####

## can't define_method on an Object

my_object = Object.new

begin
  my_object.define_method(:foo) do
    puts "foo"
  end
rescue => e
  puts "can't defined_method on an Object: #{e.message}"
end