English and symbolic boolean operators in Ruby

Learn the difference between the boolean operators and what
this has to do with short-circuit evaluation and precedence.

Transcript

1. (and  &&)    
    
   and operators
   (or  ||)
   @DonSchado | 15.01.2014
   

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2. (and  &&)    
    
   and operators
   (or  ||)
   english and symbolic boolean
   @DonSchado | 15.01.2014
   

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3. Quiztime!!! \o/
   

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4. foo  =  true  &&  "bar"
   foo  =  ?
   #=>  ?
   

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5. foo  =  "bar"
   #=>  "bar"
   foo  =  true  &&  "bar"
   

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6. foo  =  "bar"
   #=>  "bar"
   foo  =  true  &&  "bar"
   foo  =  true  and  "bar"
   foo  =  ?
   #=>  ?
   

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7. foo  =  "bar"
   foo  =  true
   #=>  "bar"
   #=>  "bar"
   foo  =  true  &&  "bar"
   foo  =  true  and  "bar"
   

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8. foo  =  42  &&  foo  *  2
   foo  =  ?
   #=>  ?
   

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9. foo  =  42  &&  foo  *  2
   foo  =  nil
   #=>  
   NoMethodError:  
   undefined  method  `*'  for  nil:NilClass
   

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10. foo  =  42  and  foo  *  2
    foo  =  ?
    #=>  ?
    foo  =  42  &&  foo  *  2
    foo  =  nil
    #=>  
    NoMethodError:  
    undefined  method  `*'  for  nil:NilClass
    

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11. foo  =  42  and  foo  *  2
    foo  =  42
    #=>  84
    foo  =  42  &&  foo  *  2
    foo  =  nil
    #=>  
    NoMethodError:  
    undefined  method  `*'  for  nil:NilClass
    

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12. short-circuit evaluation & precedence
    

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13. short-circuit evaluation
    (or McCarthy evaluation)
    ”... denotes the semantics of some Boolean
    operators [...] in which the second argument
    is only executed or evaluated if the first
    argument does not suffice to determine the
    value of the expression.”
    ”Short-circuit operators are, in effect, control
    structures rather than simple arithmetic
    operators”
    http://en.wikipedia.org/wiki/Short-circuit_evaluation
    

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14. short-circuit evaluation
    (or McCarthy evaluation)
    ”... denotes the semantics of some Boolean
    operators [...] in which the second argument
    is only executed or evaluated if the first
    argument does not suffice to determine the
    value of the expression.”
    ”Short-circuit operators are, in effect, control
    structures rather than simple arithmetic
    operators”
    http://en.wikipedia.org/wiki/Short-circuit_evaluation
    :foo  &&  :bar #=>  :bar
    

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15. short-circuit evaluation
    (or McCarthy evaluation)
    ”... denotes the semantics of some Boolean
    operators [...] in which the second argument
    is only executed or evaluated if the first
    argument does not suffice to determine the
    value of the expression.”
    ”Short-circuit operators are, in effect, control
    structures rather than simple arithmetic
    operators”
    http://en.wikipedia.org/wiki/Short-circuit_evaluation
    :foo  &&  :bar
    if  :foo
     :bar
    end
    #=>  :bar
    

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16. short-circuit evaluation
    (or McCarthy evaluation)
    ”... denotes the semantics of some Boolean
    operators [...] in which the second argument
    is only executed or evaluated if the first
    argument does not suffice to determine the
    value of the expression.”
    ”Short-circuit operators are, in effect, control
    structures rather than simple arithmetic
    operators”
    http://en.wikipedia.org/wiki/Short-circuit_evaluation
    :foo  &&  :bar
    if  :foo
     :bar
    end
    #=>  :bar
    :foo  ||  :bar #=>  :foo
    

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17. short-circuit evaluation
    (or McCarthy evaluation)
    ”... denotes the semantics of some Boolean
    operators [...] in which the second argument
    is only executed or evaluated if the first
    argument does not suffice to determine the
    value of the expression.”
    ”Short-circuit operators are, in effect, control
    structures rather than simple arithmetic
    operators”
    http://en.wikipedia.org/wiki/Short-circuit_evaluation
    :foo  &&  :bar
    if  :foo
     :bar
    end
    #=>  :bar
    :foo  ||  :bar
    if  :foo
     :foo
    else
     :bar
    end
    #=>  :foo
    

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18. precedence
    High precedence operations happen
    before low precedence operations.
    !, ~, unary +
    **
    unary -
    *, /, %
    +, -
    <>
    &
    |, ^
    >, >=, <=>, ==, ===, !=, =~, !~
    &&
    ||
    .., ...
    ?, :
    modifier-rescue
    =, +=, -=, etc.
    defined?
    not
    or, and
    modifier-if, *-unless, *-while, *-until
    { } blocks
    http://www.ruby-doc.org/core-2.0.0/doc/syntax/precedence_rdoc.html
    high
    low
    

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19. precedence
    High precedence operations happen
    before low precedence operations.
    !, ~, unary +
    **
    unary -
    *, /, %
    +, -
    <>
    &
    |, ^
    >, >=, <=>, ==, ===, !=, =~, !~
    &&
    ||
    .., ...
    ?, :
    modifier-rescue
    =, +=, -=, etc.
    defined?
    not
    or, and
    modifier-if, *-unless, *-while, *-until
    { } blocks
    http://www.ruby-doc.org/core-2.0.0/doc/syntax/precedence_rdoc.html
    high
    low
    ≠ just to make life
    more interesting
    =
    

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20. precedence
    High precedence operations happen
    before low precedence operations.
    !, ~, unary +
    **
    unary -
    *, /, %
    +, -
    <>
    &
    |, ^
    >, >=, <=>, ==, ===, !=, =~, !~
    &&
    ||
    .., ...
    ?, :
    modifier-rescue
    =, +=, -=, etc.
    defined?
    not
    or, and
    modifier-if, *-unless, *-while, *-until
    { } blocks
    http://www.ruby-doc.org/core-2.0.0/doc/syntax/precedence_rdoc.html
    high
    low
    ≠ just to make life
    more interesting
    =
    foo  =  (true  &&  "bar")
    (foo  =  true)  and  "bar"
    

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21. precedence
    High precedence operations happen
    before low precedence operations.
    !, ~, unary +
    **
    unary -
    *, /, %
    +, -
    <>
    &
    |, ^
    >, >=, <=>, ==, ===, !=, =~, !~
    &&
    ||
    .., ...
    ?, :
    modifier-rescue
    =, +=, -=, etc.
    defined?
    not
    or, and
    modifier-if, *-unless, *-while, *-until
    { } blocks
    http://www.ruby-doc.org/core-2.0.0/doc/syntax/precedence_rdoc.html
    high
    low
    ≠ just to make life
    more interesting
    =
    foo  =  (true  &&  "bar")
    (foo  =  true)  and  "bar"
    (foo  =  42)  and  (foo  *  2)
    foo  =  (42  &&  (foo  *  2))
    

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22. http://ruby-doc.org/docs/keywords/1.9/Object.html#method-i-and
    

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23. http://ruby-doc.org/docs/keywords/1.9/Object.html#method-i-or
    

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24. don‘t be afraid of and and or
    • not be suitable for regular boolean logic
    • use them for readable control-flow scenarios
    • don‘t mix them up with && and || in the same expression
    

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25. raise  "Not  ready!"  unless  ready_to_rock?
    examples
    

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26. raise  "Not  ready!"  unless  ready_to_rock? ready_to_rock?  or  raise  "Not  ready!"
    =>
    examples
    

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27. raise  "Not  ready!"  unless  ready_to_rock? ready_to_rock?  or  raise  "Not  ready!"
    =>
    examples
    next  if  widget  =  widgets.pop
    

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28. raise  "Not  ready!"  unless  ready_to_rock? ready_to_rock?  or  raise  "Not  ready!"
    =>
    examples
    next  if  widget  =  widgets.pop widget  =  widgets.pop  and  next
    =>
    

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29. @post  =  Post.find_by_name(name)  and  @post.publish!
    raise  "Not  ready!"  unless  ready_to_rock? ready_to_rock?  or  raise  "Not  ready!"
    =>
    examples
    next  if  widget  =  widgets.pop widget  =  widgets.pop  and  next
    =>
    

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30. @post  =  Post.find_by_name(name)  and  @post.publish!
    foo  =  get_foo  or  raise  "Could  not  find  foo!"
    raise  "Not  ready!"  unless  ready_to_rock? ready_to_rock?  or  raise  "Not  ready!"
    =>
    examples
    next  if  widget  =  widgets.pop widget  =  widgets.pop  and  next
    =>
    

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31. http://devblog.avdi.org/2010/08/02/using-and-and-or-in-ruby/
    http://ruby-doc.com/docs/ProgrammingRuby/html/tut_expressions.html#UG
    https://www.tinfoilsecurity.com/blog/ruby-demystified-and-vs
    http://www.ruby-doc.org/core-2.0.0/doc/syntax/precedence_rdoc.html
    http://ruby-doc.org/docs/keywords/1.9/Object.html#method-i-and
    http://blog.revathskumar.com/2013/05/short-circuit-evaluation-in-ruby.html
    

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