gistfile1.rb

class User
  def self.space
    'Top'
  end
end

module MyNamespace
  class User
    def self.space
      'Mine'
    end
  end
  User.space # => "Mine"
end

MyNamespace::User.new # => #<MyNamespace::User:0x10016b970>
User.new # => #<User:0x10016b308>

class MyNamespace::Foo
  def self.uspace
    User.space
  end
  def bar
    'batz'
  end
  def uspace
    User.space
  end
end

MyNamespace::Foo.new.bar # => "batz"
MyNamespace::Foo.uspace # => "Top"
MyNamespace::Foo.new.uspace # => "Top"

module MyNamespace
  class Bar
    def self.uspace
      User.space
    end
    def bar
      'batz'
    end
    def uspace
      User.space
    end
    def top_uspace
      ::User.space
    end
  end
end

MyNamespace::Bar.uspace # => "Mine"
MyNamespace::Bar.new.uspace # => "Mine"
MyNamespace::Bar.new.top_uspace # => "Top"