Crystal by example: Case

case is a flow control structure based on conditions. This structure allows writing multiple conditions without using multiple ifs, which makes the code cleaner.

case has the when, which gives the condition; if it is true, the code is executed. The else comes at the end in case none of the conditions are true.

The use of then allows the case structure to be written on just one line, and to compare several conditions in the same when, a comma is used.

a = 5

case a
when 3
  puts "a is two"
when 5
  puts "a is five"
else
  puts "what is 'a'?"
end

y = 5 if 3 > 2

case y
when 5
  puts "y is 5"
else
  puts "y is somenthing."
end

x = a + 5

case x
when Bool, String   then puts "It's a boolean or string."
when Int32, Float32 then puts "It's a integer or float."
end

$ crystal run case.cr

a is five
y is 5
It's a integer or float.