Case with ranges and patterns in Ruby

Introduction

Using case with ranges and patterns helps you check where a value fits in a group or matches a shape. It makes your code cleaner and easier to read.

You want to check if a number falls within certain ranges, like grades or ages.

You need to match a value against different patterns, like arrays or hashes with specific keys.

You want to replace many <code>if-elsif</code> statements with a simpler structure.

You want your code to clearly show different cases for different value groups.

Syntax

Ruby

case variable
in pattern1
  # code for pattern1
in pattern2
  # code for pattern2
else
  # code if no pattern matches
end

Use in to match patterns or ranges inside a case statement.

Ranges use start..end and match if the variable is inside that range.

Examples

This example checks which range the score fits in and prints the result.

Ruby

case score
in 0..59
  puts "Fail"
in 60..79
  puts "Pass"
in 80..100
  puts "Excellent"
else
  puts "Invalid score"
end

This example matches data if it is an array with two elements or a hash with keys name and age.

Ruby

case data
in [x, y]
  puts "Array with two elements: #{x} and #{y}"
in {name: name, age: age}
  puts "Hash with name #{name} and age #{age}"
else
  puts "Unknown format"
end

Sample Program

This program defines a method that uses case with ranges and patterns to describe the input value. It shows how different inputs match different cases.

Ruby

def describe_value(value)
  case value
  in 1..10
    "Value is between 1 and 10"
  in 11..20
    "Value is between 11 and 20"
  in [a, b]
    "Value is an array with two elements: #{a} and #{b}"
  in {name: name, age: age}
    "Value is a hash with name #{name} and age #{age}"
  else
    "Value does not match any pattern"
  end
end

puts describe_value(7)
puts describe_value(15)
puts describe_value([3, 4])
puts describe_value({name: "Alice", age: 30})
puts describe_value("hello")

Important Notes

Patterns can match arrays, hashes, and ranges to check the shape or value group.

If no pattern matches, the else block runs.

Pattern matching with case was added in Ruby 2.7 and improved in Ruby 3.x.

Summary

Case with ranges and patterns lets you check if a value fits in a range or matches a shape.

Use in inside case to match ranges like 1..10 or patterns like arrays and hashes.

This makes your code easier to read and reduces many if-elsif checks.

Practice

1.

What does the in keyword do inside a case statement in Ruby when used with ranges?

easy

A. It checks if the value falls within the given range.

B. It assigns the range to the value.

C. It creates a new range object.

D. It compares the value for equality with the range.

Solution

1. Step 1: Understand the role of in in case

   The in keyword is used to match a value against a pattern or range inside a case statement.

2. Step 2: Check how it works with ranges

   When used with a range like 1..10, it checks if the value lies within that range.

3. Final Answer:

   It checks if the value falls within the given range. -> Option A

4. Quick Check:

   in with range means value in range [OK]

Hint: Remember: in checks membership in range or pattern [OK]

Common Mistakes:

• Thinking in assigns values instead of matching
• Confusing range equality with membership
• Assuming in creates new objects

2.

Which of the following is the correct syntax to match a number n in the range 5 to 15 inside a case statement using pattern matching?

case n
  in ???
    puts "In range"
  else
    puts "Out of range"
end

easy

A. in (5..15)

B. 5..15

C. 5...15

D. in 5..15

Solution

1. Step 1: Identify correct pattern syntax in in clause

   Inside case, in is followed directly by the pattern, so in 5..15 is correct syntax.

2. Step 2: Check other options for syntax errors

   Options without in or with extra parentheses are invalid syntax in this context.

3. Final Answer:

   in 5..15 -> Option D

4. Quick Check:

   Use in followed by the pattern without extra keywords or parentheses [OK]

Hint: Use in once, then the pattern without extra keywords [OK]

Common Mistakes:

• Writing in in 5..15 which is invalid
• Adding parentheses around the range
• Using three-dot range 5...15 which excludes 15

3.

What will be the output of this Ruby code?

score = 75
case score
in 0..49 then puts "Fail"
in 50..79 then puts "Pass"
in 80..100 then puts "Excellent"
else puts "Invalid"
end

medium

A. Pass

B. Fail

C. Excellent

D. Invalid

Solution

1. Step 1: Check which range includes 75

   75 is not in 0..49 but is in 50..79.

2. Step 2: Match the corresponding output

   The code prints "Pass" when score is in 50..79.

3. Final Answer:

   Pass -> Option A

4. Quick Check:

   75 in 50..79 means output "Pass" [OK]

Hint: Find which range includes the value, then pick that output [OK]

Common Mistakes:

• Choosing "Fail" because 75 is greater than 49
• Confusing inclusive and exclusive ranges
• Ignoring the order of case branches

4.

Identify the error in this Ruby code snippet using case with pattern matching:

value = 10
case value
in 1..5
  puts "Low"
in 6..10
  puts "Medium"
else
  puts "High"
end

medium

A. Missing then after in clauses

B. No error; code runs and prints "Medium"

C. Ranges should be written as arrays inside in

D. The case statement should use when instead of in

Solution

1. Step 1: Check syntax of case with in and ranges

   Using in with ranges inside case is valid Ruby syntax.

2. Step 2: Verify output for value 10

   10 matches the range 6..10, so it prints "Medium".

3. Final Answer:

   No error; code runs and prints "Medium" -> Option B

4. Quick Check:

   in with ranges works fine [OK]

Hint: Remember in works like when for pattern matching [OK]

Common Mistakes:

• Thinking then is mandatory after in
• Confusing in with when
• Trying to write ranges as arrays

5.

Given this Ruby code, what will be the output?

data = [3, 7, 12, 18]
case data
in [Integer, Integer, Integer, Integer]
  puts "All integers"
in [Integer, Integer, Integer, 18]
  puts "Last is 18"
else
  puts "No match"
end

hard

A. No match

B. Last is 18

C. All integers

D. SyntaxError

Solution

1. Step 1: Understand array pattern matching order

   The case checks patterns in order. The first pattern matches any array of four integers.

2. Step 2: Check if data matches first pattern

   Data is [3,7,12,18], all integers, so it matches the first pattern.

3. Step 3: Confirm second pattern is not reached

   Since first pattern matches, second is skipped.

4. Final Answer:

   All integers -> Option C

5. Quick Check:

   First matching pattern runs, so output is "All integers" [OK]

Hint: Patterns checked top-down; first match wins [OK]

Common Mistakes:

• Assuming second pattern runs despite first matching
• Confusing element types with values in patterns
• Expecting syntax error due to pattern complexity