Ruby Koans - String

  def test_the_shovel_operator_modifies_the_original_string
    original_string = "Hello, "
    hi = original_string
    there = "World"
    hi << there
    assert_equal "Hello, World", original_string

    # THINK ABOUT IT:
    #
    # Ruby programmers tend to favor the shovel operator (<<) over the
    # plus equals operator (+=) when building up strings.  Why?
  end

主要是在講用了hi = original_string 之後改變hi裡面的值會連original_string的值也一起改了
Ruby裡面這些都是reference,hi = original_string 之後他們兩個就會參照到同一個物件

2.3.1 :121 > original_string.object_id
 => 70169322460680
2.3.1 :122 > hi.object_id
 => 70169322460680

如果今天是用+=的話,因為這是一個assignment,他們的object_id就會不一樣了

2.3.1 :112 >     original_string = "Hello, "
 => "Hello, "
2.3.1 :113 >     hi = original_string
 => "Hello, "
2.3.1 :114 >     there = "World"
 => "World"
2.3.1 :115 > hi += there
 => "Hello, World"
2.3.1 :116 > hi
 => "Hello, World"
2.3.1 :117 > original_string
 => "Hello, "

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