Symbol type and immutability in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using symbols?

Consider the following Ruby code snippet. What will it print?

Ruby

sym1 = :hello
sym2 = :hello
puts sym1.object_id == sym2.object_id

A SyntaxError

B true

C false

D nil

💡 Hint

Symbols with the same name share the same object in memory.

In Ruby, symbols are immutable and unique. Two symbols with the same name point to the same object, so their object_ids are equal.

❓ Predict Output

intermediate

What happens when you try to modify a symbol?

What error will this Ruby code produce?

Ruby

sym = :example
sym[0] = 'E'

A NoMethodError: undefined method `[]=' for Symbol

B RuntimeError: can't modify symbol

C TypeError: no implicit conversion of String into Integer

D SyntaxError

💡 Hint

Symbols do not support string-like modification methods.

Symbols are immutable and do not have methods like []= to modify them. Trying to call []= on a symbol raises NoMethodError.

🧠 Conceptual

advanced

Why are symbols considered immutable in Ruby?

Which of the following best explains why symbols are immutable?

A Because Ruby automatically freezes all objects of type Symbol

B Because symbols are stored as strings internally and strings are immutable

C Because symbols are unique and shared, changing one would affect all references

D Because symbols are garbage collected immediately after creation

💡 Hint

Think about what would happen if you changed a symbol's value.

Symbols are immutable because they are unique and shared across the program. Changing one symbol would change all references, which is not allowed.

❓ Predict Output

advanced

What is the output of this code comparing symbols and strings?

What will this Ruby code print?

Ruby

puts :ruby == 'ruby'
puts :ruby.eql?('ruby')

A

false
false

B

true
true

C

false
true

D

true
false

💡 Hint

Symbols and strings are different types even if they look similar.

Symbols and strings are different objects and types in Ruby. Comparing them with == or eql? returns false.

❓ Predict Output

expert

How many unique objects are created in this Ruby code?

How many unique objects are created after running this code?

Ruby

arr = [:a, :b, :a, :c, :b]
unique = arr.uniq
puts unique.size

A 2

B 5

C 4

D 3

💡 Hint

uniq removes duplicates from the array.

The array has symbols :a, :b, :a, :c, :b. The unique symbols are :a, :b, and :c, so size is 3.