english and symbolic boolean operators in ruby

(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


foo = 42 and foo * 2

foo = 42

#=> 84

foo = 42 && foo * 2

foo = nil


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

http://en.wikipedia.org/wiki/Logical_connective




http://en.wikipedia.org/wiki/Control_structure










:foo && :bar #=> :bar















:foo && :bar

if :foo :barend

#=> :bar















:foo && :bar

if :foo :barend

#=> :bar

:foo || :bar #=> :foo















:foo && :bar

if :foo :barend

#=> :bar

:foo || :bar

if :foo :fooelse :barend

#=> :foo











precedenceHigh precedence operations happen before low precedence operations.

!, ~, unary +**unary -*, /, %+, -<<, >>&|, ^>, >=, <, <=<=>, ==, ===, !=, =~, !~&&||.., ...?, :modifier-rescue=, +=, -=, etc.defined?notor, andmodifier-if, *-unless, *-while, *-until{ } blocks

http://www.ruby-doc.org/core-2.0.0/doc/syntax/precedence_rdoc.html

high

low






high

low

≠ just to make life more interesting

=






high

low


=

foo = (true && "bar")

(foo = true) and "bar"






high

low


=

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


examples

next if widget = widgets.pop


examples

next if widget = widgets.pop widget = widgets.pop and next=>

@post = Post.find_by_name(name) and @post.publish!


examples


@post = Post.find_by_name(name) and @post.publish!

foo = get_foo or raise "Could not find foo!"


examples


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://blog.revathskumar.com/2013/05/short-circuit-evaluation-in-ruby.html













english and symbolic boolean operators in ruby

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