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

Challenge - 5 Problems

❓ Predict Output

intermediate

Understanding == vs equal? with strings

What is the output of this Ruby code?

Ruby

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

A

false
true

B

true
false

C

true
true

D

false
false

💡 Hint

Remember that == checks value equality, while equal? checks if both variables point to the same object.

The == operator compares the content of the strings, so it returns true because both strings have the same characters.

The equal? method checks if both variables refer to the exact same object in memory. Since a and b are two different string objects with the same content, equal? returns false.

❓ Predict Output

intermediate

Object identity with integers

What will this Ruby code print?

Ruby

x = 1000
y = 1000
puts x == y
puts x.equal?(y)

A

true
false

B

true
true

C

false
false

D

false
true

💡 Hint

Check how Ruby handles integers and object identity for large numbers.

The == operator compares the values, so it returns true because both x and y are 1000.

The equal? method checks if both variables point to the same object. For integers larger than a certain range, Ruby creates separate objects, so equal? returns false.

❓ Predict Output

advanced

Comparing symbols with == and equal?

What is the output of this Ruby code?

Ruby

sym1 = :ruby
sym2 = :ruby
puts sym1 == sym2
puts sym1.equal?(sym2)

A

true
false

B

false
false

C

false
true

D

true
true

💡 Hint

Symbols are unique and immutable in Ruby.

Symbols with the same name are the same object in Ruby.

Therefore, both == and equal? return true.

❓ Predict Output

advanced

Effect of dup on object identity

What does this Ruby code print?

Ruby

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

A

true
false

B

true
true

C

false
false

D

false
true

💡 Hint

dup creates a shallow copy of the object.

The == operator compares the content of the arrays, which are the same, so it returns true.

The equal? method checks if both variables point to the same object. Since dup creates a new object, equal? returns false.

❓ Predict Output

expert

Mutable objects and identity after modification

What is the output of this Ruby code?

Ruby

str1 = "hello"
str2 = str1
str2 << " world"
puts str1
puts str2
puts str1.equal?(str2)

A

hello
hello
true

B

hello
hello world
false

C

hello world
hello world
true

D

hello world
hello world
false

💡 Hint

Remember that modifying str2 affects str1 if they reference the same object.

Both str1 and str2 point to the same string object.

Appending " world" to str2 modifies the object itself, so str1 also shows the change.

equal? returns true because both variables reference the same object.