Object identity (equal? vs ==) in Ruby - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if two strings have the same content using the correct operator.

Ruby

str1 = "hello"
str2 = "hello"
puts str1 [1] str2

Drag options to blanks, or click blank then click option'

A==

Bequal?

C===

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using equal? instead of == to compare content.

In Ruby, == checks if two objects have the same content.

2fill in blank

medium

Complete the code to check if two variables point to the exact same object.

Ruby

a = "ruby"
b = a
puts a.[1](b)

Drag options to blanks, or click blank then click option'

A==

B===

Cequal?

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using == instead of equal? to check object identity.

The equal? method checks if two variables reference the same object in memory.

3fill in blank

hard

Fix the error in the code to correctly check if two arrays are the same object.

Ruby

arr1 = [1, 2, 3]
arr2 = [1, 2, 3]
puts arr1.[1](arr2)

Drag options to blanks, or click blank then click option'

A==

B===

C!=

Dequal?

Attempts:

3 left

💡 Hint

Common Mistakes

Using == which returns true for arrays with same content but different objects.

To check if two arrays are the exact same object, use equal?. Using == checks content equality.

4fill in blank

hard

Fill both blanks to create a hash that maps strings to their object identity check results.

Ruby

str1 = "test"
str2 = "test"
result = { str1: str1 [1] str2, str2: str1.[2](str2) }

Drag options to blanks, or click blank then click option'

A==

Bequal?

C===

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up == and equal? in the hash values.

The first blank uses == to check content equality, the second uses equal? to check object identity.

5fill in blank

hard

Fill all three blanks to create a method that returns true if two objects have the same content but are different objects.

Ruby

def same_content_different_object?(obj1, obj2)
  obj1 [1] obj2 && !obj1.[2](obj2) && obj1 [3] obj2
end

Drag options to blanks, or click blank then click option'

A==

Bequal?

Cis_a?

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using equal? instead of == for content comparison.

This method checks if obj1 and obj2 have the same content (==), are not the same object (!equal?), and are not unequal (!= used to confirm difference).

Practice

1. In Ruby, what does the method equal? check between two objects?

easy

A. If both objects respond to the same methods

B. If both objects have the same content or value

C. If both variables point to the exact same object in memory

D. If both objects are of the same class

Solution

1. Step 1: Understand equal? method purpose

   The equal? method checks if two variables reference the exact same object in memory, not just if they look alike.

2. Step 2: Compare with other methods

   Unlike ==, which compares content, equal? is about object identity.

3. Final Answer:

   If both variables point to the exact same object in memory -> Option C

4. Quick Check:

   equal? checks object identity = D [OK]

Hint: Remember: equal? means same object, not just same value [OK]

Common Mistakes:

• Confusing equal? with ==
• Thinking equal? compares content
• Assuming equal? checks class type

2. Which of the following Ruby code snippets correctly uses equal? to check if two variables refer to the same object?

easy

A. a.equal?(b)

B. a == b

C. a.equals(b)

D. equal?(a, b)

Solution

1. Step 1: Recall correct syntax for equal?

   The method equal? is called on one object and passed another as an argument, like a.equal?(b).

2. Step 2: Identify incorrect options

   a == b uses content equality, a.equals(b) is not a Ruby method, and equal?(a, b) is invalid syntax.

3. Final Answer:

   a.equal?(b) -> Option A

4. Quick Check:

   Correct equal? syntax = B [OK]

Hint: Use object.equal?(other_object) syntax [OK]

Common Mistakes:

• Using == instead of equal?
• Writing equals instead of equal?
• Calling equal? as a standalone function

3. What will be the output of the following Ruby code?

a = "hello"
b = "hello"
puts a == b
puts a.equal?(b)

medium

A. true
true

B. true
false

C. false
true

D. false
false

Solution

1. Step 1: Evaluate a == b

   Both a and b are strings with the same content "hello", so a == b returns true.

2. Step 2: Evaluate a.equal?(b)

   Though content is same, a and b are different string objects, so equal? returns false.

3. Final Answer:

   true false -> Option B

4. Quick Check:

   == compares content, equal? compares object identity = C [OK]

Hint: == checks value, equal? checks same object [OK]

Common Mistakes:

• Assuming equal? returns true for identical strings
• Confusing output order
• Thinking == checks object identity

4. Consider this Ruby code snippet:

arr1 = [1, 2, 3]
arr2 = arr1
arr3 = [1, 2, 3]

puts arr1.equal?(arr2)
puts arr1.equal?(arr3)

What is the output and why?

medium

A. false
false

B. false
true

C. true
true

D. true
false

Solution

1. Step 1: Analyze arr1.equal?(arr2)

   Since arr2 is assigned directly from arr1, both point to the same object, so equal? returns true.

2. Step 2: Analyze arr1.equal?(arr3)

   arr3 is a new array with the same content but a different object, so equal? returns false.

3. Final Answer:

   true false -> Option D

4. Quick Check:

   Same object = true, same content but different object = false [OK]

Hint: Assignment copies object reference; new array creates new object [OK]

Common Mistakes:

• Assuming arrays with same content are the same object
• Confusing == with equal?
• Thinking assignment creates a new object

5. You want to check if two variables x and y refer to the same object, but x might be nil. Which Ruby code safely performs this check without errors?

hard

A. x.equal?(y)

B. y.equals(x)

C. x&.equal?(y)

D. x == y

Solution

1. Step 1: Check safety of equal? on nil

   In Ruby, nil is an object and responds to equal?, so x.equal?(y) is safe even if x is nil. It returns false unless y is also nil.

2. Step 2: Eliminate distractors

   x&.equal?(y) returns nil if x is nil, which is not a proper boolean result. y.equals(x) calls a non-existent method. x == y checks content, not identity.

3. Final Answer:

   x.equal?(y) -> Option A

4. Quick Check:

   nil.equal?(y) safe boolean check = C [OK]

Hint: Even nil.equal?(other) works without error [OK]

Common Mistakes:

• Using &. which returns nil instead of boolean
• Calling non-existent equals method
• Using == which checks content, not identity