Spaceship operator (<=>) in Ruby - Mini Project: Build & Apply

Using the Spaceship Operator (<=>) in Ruby

📖 Scenario: You are working on a simple ranking system for a game. You want to compare players' scores to see who is higher, lower, or if they are equal.

🎯 Goal: Build a Ruby program that uses the spaceship operator () to compare two player scores and print the comparison result.

📋 What You'll Learn

Create two integer variables named score1 and score2 with exact values 85 and 90 respectively.

Create a variable called comparison that stores the result of score1 <=> score2.

Use a case statement with comparison to print "score1 is less than score2", "score1 is equal to score2", or "score1 is greater than score2" based on the comparison result.

Print the final message to the console.

💡 Why This Matters

🌍 Real World

Comparing scores or rankings is common in games, leaderboards, and sorting lists.

💼 Career

Understanding comparison operators like the spaceship operator helps in writing clean and efficient sorting and comparison logic in software development.

1

Create the player scores

Create two integer variables called score1 and score2 with the exact values 85 and 90 respectively.

Ruby

# Create two variables score1 and score2 with values 85 and 90
# Your code here

Hint

Use = to assign values to variables like score1 = 85.

2

Compare the scores using the spaceship operator

Create a variable called comparison that stores the result of score1 <=> score2.

Ruby

score1 = 85
score2 = 90
# Create a variable comparison that stores score1  score2
# Your code here

Hint

The spaceship operator returns -1, 0, or 1 depending on how the two values compare.

3

Use a case statement to interpret the comparison

Use a case statement with the variable comparison to print "score1 is less than score2" if comparison is -1, "score1 is equal to score2" if 0, and "score1 is greater than score2" if 1.

Ruby

score1 = 85
score2 = 90
comparison = score1  score2
# Use a case statement with comparison to print the correct message
# Your code here

Hint

The case statement helps you run different code depending on the value of comparison.

4

Print the comparison result

Run the program to print the message that shows how score1 compares to score2.

Ruby

score1 = 85
score2 = 90
comparison = score1  score2
case comparison
when -1
  puts "score1 is less than score2"
when 0
  puts "score1 is equal to score2"
when 1
  puts "score1 is greater than score2"
end
# Run the program to print the result
# Your code here

Hint

Just run the program. The puts statements inside the case will print the message.

Practice

1.

What does the Ruby spaceship operator <=> return when comparing two values?

easy

A. true if left is smaller, false if equal, nil if left is bigger

B. -1 if left is smaller, 0 if equal, 1 if left is bigger

C. The sum of both values

D. A boolean indicating if values are equal

Solution

1. Step 1: Understand the spaceship operator purpose

   The spaceship operator compares two values and returns an integer indicating their order.

2. Step 2: Recall the return values

   It returns -1 if the left value is smaller, 0 if both are equal, and 1 if the left is bigger.

3. Final Answer:

   -1 if left is smaller, 0 if equal, 1 if left is bigger -> Option B

4. Quick Check:

   Spaceship operator returns -1, 0, or 1 [OK]

Hint: Remember: -1 smaller, 0 equal, 1 bigger [OK]

Common Mistakes:

• Confusing return values with booleans
• Thinking it returns a sum or boolean
• Mixing up which side is compared

2.

Which of the following is the correct syntax to compare a and b using the spaceship operator in Ruby?

?

easy

A. a => b

B. a =< b

C. a <= b

D. a <=> b

Solution

1. Step 1: Identify the spaceship operator syntax

   The spaceship operator is written as <=> between two values.

2. Step 2: Match the correct syntax

   Only a <=> b uses the correct operator symbol and order.

3. Final Answer:

   a <=> b -> Option D

4. Quick Check:

   Correct operator is <=> [OK]

Hint: Look for <=> exactly between variables [OK]

Common Mistakes:

• Using => which is a hash rocket
• Using <= or =< which are comparison operators
• Swapping operator symbols incorrectly

3.

What is the output of the following Ruby code?

puts 5 <=> 10
puts 10 <=> 10
puts 15 <=> 10

medium

A. false
true
false

B. 1
0
-1

C. -1
0
1

D. 10
10
10

Solution

1. Step 1: Evaluate each comparison

   5 <=> 10 returns -1 because 5 is smaller than 10.
   10 <=> 10 returns 0 because both are equal.
   15 <=> 10 returns 1 because 15 is bigger than 10.

2. Step 2: Confirm output lines

   Each puts prints the result on a new line, so output is three lines: -1, 0, 1.

3. Final Answer:

   -1 0 1 -> Option C

4. Quick Check:

   5 < 10 = -1, equal = 0, 15 > 10 = 1 [OK]

Hint: Remember: smaller = -1, equal = 0, bigger = 1 [OK]

Common Mistakes:

• Mixing up the order of output
• Expecting boolean true/false instead of -1,0,1
• Confusing <=> with < or > operators

4.

Identify the error in this Ruby code snippet using the spaceship operator:

result = 7 <=>
3
puts result

medium

A. Syntax error due to line break in operator

B. Returns nil because 7 and 3 are not comparable

C. Returns 1 as expected

D. Runtime error due to undefined variable

Solution

1. Step 1: Check operator usage across lines

   The spaceship operator <=> must be on the same line between operands; splitting it causes syntax error.

2. Step 2: Understand Ruby syntax rules

   Ruby does not allow breaking operators across lines without proper continuation, so this code raises a syntax error.

3. Final Answer:

   Syntax error due to line break in operator -> Option A

4. Quick Check:

   Operators must not be split across lines [OK]

Hint: Keep <=> on one line between values [OK]

Common Mistakes:

• Splitting operator across lines
• Assuming nil return for invalid syntax
• Confusing runtime errors with syntax errors

5.

Given the array arr = [3, 1, 4, 1, 5], which code snippet correctly sorts the array in descending order using the spaceship operator?

hard

A. arr.sort { |a, b| b <=> a }

B. arr.sort { |a, b| a == b }

C. arr.sort_by { |x| x <=> 0 }

D. arr.sort { |a, b| a <=> b }

Solution

1. Step 1: Understand sorting with spaceship operator

   The block compares two elements a and b. To sort descending, compare b to a.

2. Step 2: Analyze each option

   arr.sort { |a, b| a <=> b } sorts ascending (a <=> b).
   arr.sort { |a, b| b <=> a } sorts descending (b <=> a).
   arr.sort_by { |x| x <=> 0 } misuses sort_by with spaceship operator.
   arr.sort { |a, b| a == b } returns boolean, invalid for sorting.

3. Final Answer:

   arr.sort { |a, b| b <=> a } -> Option A

4. Quick Check:

   Reverse order uses b <=> a [OK]

Hint: Reverse order: swap a and b in <=> [OK]

Common Mistakes:

• Using a <=> b for descending sort
• Misusing sort_by with spaceship operator
• Returning boolean instead of integer in block