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

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

Quiztime!!! \o/ 

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

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

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

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

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

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

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

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

short-circuit evaluation & precedence 

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 

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 

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 

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 

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 

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 

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 = 

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" 

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)) 

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

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

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 

raise  "Not  ready!"  unless  ready_to_rock? examples 

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

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

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 => 

@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 => 

@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 => 

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