Nested function definitions are a bad idea in Ruby.

def.shard.rb

#!/usr/bin/env ruby -w

def defit
  def ohai
    puts "hello from #{self.class.inspect} #{self.inspect}"
  end

  puts "called defit in #{self.class.inspect} #{self.inspect}"
end

module MyModule
  defit
end

:whatever.ohai

i_like_this_best.rb

#!/usr/bin/env ruby -w

module YourModule

	def self.defit
		ohai = ->() { puts "hello from #{self.class.inspect} #{self.inspect}" }

	  puts "called defit in #{self.class.inspect} #{self.inspect}"
	end

end

YourModule.defit

:whatever.ohai
#=> fails (yay!)

inside_a_different_module.rb

#!/usr/bin/env ruby -w

module YourModule

	def self.defit
	  def ohai
	    puts "hello from #{self.class.inspect} #{self.inspect}"
	  end

	  puts "called defit in #{self.class.inspect} #{self.inspect}"
	end

end

YourModule.defit

:whatever.ohai
#=> fails (yay)

without_using_the_module_even.rb

#!/usr/bin/env ruby -w

def defit
  def ohai
    puts "hello from #{self.class.inspect} #{self.inspect}"
  end

  puts "called defit in #{self.class.inspect} #{self.inspect}"
end

# module MyModule
  defit
# end

:whatever.ohai
#=> works (boo)

inside_a_different_module is subtly wrong, too… it defines ohai as an instance method on YourModule rather than leaving it local to the body of defit