How to Use Case When in Ruby: Simple Guide with Examples

In Ruby, use case with when to check a value against multiple conditions cleanly. The syntax is case variable; when value1 then ...; when value2 then ...; else ...; end. It works like a simpler alternative to many if-elsif statements.

Syntax

The case statement evaluates an expression once and compares it with each when clause. If a match is found, the corresponding code runs. The else clause is optional and runs if no matches occur.

• case expression: The value to compare.
• when value: Checks if expression equals this value.
• then: Optional keyword to put code on the same line.
• else: Runs if no when matches.
• end: Closes the case block.

ruby

case expression
when value1
  # code if expression === value1
when value2 then
  # code if expression === value2
else
  # code if no match
end

Example

This example shows how to use case when to print a message based on a day of the week.

ruby

day = "Tuesday"

case day
when "Monday"
  puts "Start of the work week"
when "Tuesday"
  puts "Second day of the week"
when "Friday"
  puts "Almost weekend!"
else
  puts "Just another day"
end

Output

Second day of the week

Common Pitfalls

One common mistake is forgetting the end keyword to close the case block. Another is using when without a matching case. Also, case compares with ===, so be careful with types and ranges.

Example of a wrong and right way:

ruby

# Wrong: missing end
# case x
# when 1
#   puts "One"

# Right:
case x
when 1
  puts "One"
end

Quick Reference

Keyword	Purpose
case	Starts the case statement with an expression to compare
when	Defines a condition to match against the case expression
then	Optional, separates condition and code on the same line
else	Runs if no when condition matches
end	Ends the case statement

Key Takeaways

Use case when to simplify multiple condition checks in Ruby.

Remember to close the case block with end.

The case statement uses === for comparison, so it works with ranges and classes.

The else clause is optional but useful for default cases.

Use then for concise one-line when statements.