Question

Why does the second assert_equal below work? How does ruby associate “dos” with :two?

  def test_default_value

    hash2 = Hash.new("dos")
    hash2[:one] = 1

    assert_equal 1, hash2[:one]
    assert_equal "dos", hash2[:two]
  end

Answer 1

The argument to Hash.new is the “default” value – when a key isn’t present, and is read, return that value instead. You can also pass a block to Hash.new to have more complex behaviour around default values.

http://ruby-doc.org/core-1.8.7/Hash.html#method-c-new