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

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

2. and
(and
&&)
(or
||) operators
olic boolean
nglish and symb
e
@DonSchado | 15.01.2014

3. Quiztime!!! o/

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

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

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

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

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

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

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

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

12. short-circuit evaluation & precedence

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

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

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

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
#=>
:bar
if
:foo
:bar
end
:foo
||
:bar
#=>
:foo

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
#=>
:bar
if
:foo
:bar
end
:foo
||
:bar
if
:foo
:foo
else
:bar
end
#=>
:foo

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

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

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

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

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

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

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

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

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

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

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

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

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

31. http://www.ruby-doc.org/core-2.0.0/doc/syntax/precedence_rdoc.html
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://ruby-doc.org/docs/keywords/1.9/Object.html#method-i-and
http://blog.revathskumar.com/2013/05/short-circuit-evaluation-in-ruby.html