Ruby Quiz

at 学生エンジニア限定LT大会

Transcript

1. Ruby Quiz
   Oct. 8, 2017
   第4回 学生エンジニア限定LT大会
   

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2. I have only 5 minutes,
   so I'll speak very fast.
   

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3. Self introduction
   ● Pocke
   ● Actcat, Inc. / SideCI
   ● RuboCop' s core developer
   ● Student at The Open University of Japan
   

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4. SideCI
   

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5. Automated Code Review
   as a Service
   

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6. Please access here! https://sideci.com
   

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7. Ruby Quiz
   

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8. Question
   

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9. Do you write Ruby?
   

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10. Ruby Quiz
    ● You are a Ruby interpreter.
    ○ You are a parse.y.
    ○ You are a YARV.
    ● You execute ruby code, and you output result.
    

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11. Quiz 1
    

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12. Q. What does the code output?
    p(??)
    p(%_?_)
    

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13. Answer
    p(??) # => "?"
    p(%_?_) # => "?"
    

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14. Why?
    

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15. A. Why does it output "?"?
    p(??)
    p(%_?_)
    %…
    is a string literal.
    e.g.) %_?_ == "?" , %!???! == "???"
    ?_ is a character literal.
    e.g.) ?_ == "_" , ?? == "?"
    

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16. Quiz 2
    

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17. Q. What does the code output?
    p(????::?:)
    p(% %s% %%%%)
    

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18. Answer
    p(????::?:) # => ":"
    p(% %s% %%%%) # => "%"
    

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19. Why????
    

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20. Answer
    p(????::?:)
    p(% %s% %%%%)
    1. ?? is "?"
    2. ? is a part of conditional op
    3. ?: is ":"
    4. : is a part of conditional op
    5. ?: is ":"
    "?" ? ":" : ":"
    1. % %s% is "%s%"
    2. % is a format op(Like sprintf)
    3. %%% is ""
    sprintf("%s%", "")
    

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21. Quiz 3
    

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22. Q. What does the code output?
    a = ["1","2","3"]
    a&.map(&:to_i)&.&([1])
    

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23. Answer
    a = ["1","2","3"]
    a&.map(&:to_i)&.&([1])
    # => [1]
    

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24. Why?????
    

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25. Answer
    a = ["1","2","3"]
    a&.map(&:to_i)&.&([1])
    # => [1]
    &. is a safe navigation op(nil guard).
    &:to_i is an implicit to_proc
    op.
    A safe
    navigation op & is an intersection op call
    (like [1,2,3] & [1])
    

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26. Conclusion
    

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27. ● We can write tricky code in Ruby.
    ○ Very fun!!!
    Thank you for listening!
    Conclusion
    

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