Conditional structures/Ruby: Difference between revisions

 

===if-then-else===

foo

elsif s == 'Bye World'

else

deus_ex

 

Note that <code>if...end</code> is an expression, so its return value can be captured in a variable:

 

s = 'yawn'

result = if s == 'Hello World'

:deus_ex

end

 

===ternary===

 

===case-when-else===

A generic case statement

when Time.now.wday == 5

puts "TGIF"

else

puts "nothing special here"

or, comparing to a specific object

when 'Tom'

chase

when 'Jerry'

flee

 

For the second case, the comparisions are preformed using the <code>===</code> "case equality" method like this: <code>'Tom' === cartoon_character</code>. The default behaviour of <code>===</code> is simple <code>Object#==</code> but some classes define it differently. For example the Module class (parent class of Class) defines <code>===</code> to return true if the class of the target is the specified class or a descendant:

when Numeric

puts "I'm a number. My absolute value is #{some_object.abs}"

else

puts "I'm a #{some_object.class}"

 

The class Regexp aliases <code>===</code> to <code>=~</code> so you can write a case block to match against some regexes

when /\A\Z/ then puts "Empty"

when /\A[[:lower:]]+\Z/ then puts "Lower case"

when /\A[[:upper:]]+\Z/ then puts "Upper case"

else then puts "Mixed case or not purely alphabetic"

 

The class Range aliases <code>===</code> to <code>include?</code>:

when 1..50 then puts "low"

when 51..75 then puts "medium"

when 76..100 then puts "high"