Conditional structures/Ruby

From Rosetta Code
Conditional structures/Ruby is part of Conditional Structures. You may find other members of Conditional Structures at Category:Conditional Structures.

if-then-else[edit]

if s == 'Hello World'
foo
elsif s == 'Bye World'
bar
else
deus_ex
end

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

 
s = 'yawn'
result = if s == 'Hello World'
:foo
elsif s == 'Bye World'
:bar
else
:deus_ex
end
# result now holds the symbol :deus_ex

ternary[edit]

 s == 'Hello World' ? foo : bar

case-when-else[edit]

A generic case statement

case
when Time.now.wday == 5
puts "TGIF"
when rand(3) == 2
puts "had a 33% chance of being right"
else
puts "nothing special here"
end

or, comparing to a specific object

case cartoon_character
when 'Tom'
chase
when 'Jerry'
flee
end

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

case some_object
when Numeric
puts "I'm a number. My absolute value is #{some_object.abs}"
when Array
puts "I'm an array. My length is #{some_object.length}"
when String
puts "I'm a string. When I'm down I look like this: #{some_object.downcase}"
else
puts "I'm a #{some_object.class}"
end

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

case astring
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"
end

The class Range aliases === to include?:

case 79
when 1..50 then puts "low"
when 51..75 then puts "medium"
when 76..100 then puts "high"
end