Ruby Trivia

Presented at the Berlin Ruby User Group (RUG::B) on October 1, 2015.

Transcript

1. Ruby
   Trivia
   

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2. In Ruby, a dash may not be used in a
   variable name…
   …but before Ruby 2.1, one variable
   was allowed to be named with a dash.
   What was it called?
   Question 1:
   

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3. In Ruby, a dash may not be used in a
   variable name…
   …but before Ruby 2.1, one variable
   was allowed to be named with a dash.
   What was it called?
   Hint: It’s a global variable.
   Question 1:
   

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4. $-
   Answer 1:
   

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5. Why can’t variable names
   contain dashes?
   Bonus Question:
   

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6. Why can’t variable names
   contain dashes?
   Bonus Question:
   Answer: Because the Ruby parser can’t distinguish it from the
   minus (-) operator between two variables (e.g. forty-two).
   

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7. Ruby may define a special File
   object in the first file it interprets.
   What is it called?
   What does it do?
   Question 2:
   

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8. Ruby may define a special File
   object in the first file it interprets.
   What is it called?
   Question 2:
   Hint: When you call read, it reads the file, starting after
   __END__
   

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9. DATA
   Answer 2:
   

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10. What happens if you call:
    DATA.rewind
    before
    DATA.read
    Bonus Question:
    

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11. What happens if you call:
    DATA.rewind
    before
    DATA.read
    Bonus Question:
    Answer: It reads the entire file, including the source code.
    

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12. The following line of code is
    valid Ruby syntax:
    a = true && return

    But this line of code is not:
    a = return && true
    What is the error message?
    Question 3:
    

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13. void value
    expression
    Answer 3:
    

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14. When you convert the range:
    (1..3).to_a
    You get the array:

    [1, 2, 3]

    What is the result of:
    (3..1).to_a
    Question 4:
    

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15. []
    Answer 4:
    

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16. What method would need to be
    added to the Range interface to
    make descending sequences
    possible?
    Bonus Question:
    

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17. What method would need to be
    added to the Range interface to
    make descending sequences
    possible?
    Bonus Question:
    Answer: pred (the opposite of succ).
    

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18. What Ruby class mixes-in
    Comparable but doesn’t define
    the spaceship (<=>) operator?
    Question 5:
    

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19. What Ruby class mixes-in
    Comparable but doesn’t define
    the spaceship (<=>) operator?
    Hint: It’s a descendant of Numeric.
    Question 5:
    

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20. Complex
    Answer 5:
    

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21. Thanks for playing!
    Follow @sferik on Twitter for
    more Ruby trivia and practica.
    

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