Symbol type and immutability in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a symbol named :apple.

Ruby

fruit = [1]

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

A'apple'

B:apple

Capple

D"apple"

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes creates a string, not a symbol.

Leaving out the colon creates a variable or method name.

The colon : before a word creates a symbol in Ruby. So :apple is a symbol.

2fill in blank

medium

Complete the code to check if two symbols are the same object.

Ruby

puts :cat.[1] :cat

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

A!=

B==

Ceql?

Dequal?

Attempts:

3 left

💡 Hint

Common Mistakes

Using == checks value equality but not object identity.

Using != is for inequality.

The equal? method checks if two objects are the exact same object in memory. Symbols with the same name are the same object.

3fill in blank

hard

Fix the error in the code to convert a string to a symbol.

Ruby

sym = "dog".[1]

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

Ato_sym!

Bto_s

Cto_sym

Dto_str

Attempts:

3 left

💡 Hint

Common Mistakes

Using to_s returns a string, not a symbol.

There is no to_sym! method.

The method to_sym converts a string to a symbol in Ruby.

4fill in blank

hard

Fill both blanks to create a hash with symbol keys and access a value.

Ruby

person = { [1] => "Alice", [2] => 30 }
age = person[:age]

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

A:name

B:age

C"age"

D"name"

Attempts:

3 left

💡 Hint

Common Mistakes

Using strings as keys when symbols are expected.

Mixing symbol and string keys inconsistently.

Symbols are used as keys in hashes for efficiency. Here, :name and :age are symbol keys.

5fill in blank

hard

Fill all three blanks to demonstrate symbol immutability and comparison.

Ruby

sym1 = :car
sym2 = :car
puts sym1 [1] sym2
puts sym1.object_id [2] sym2.object_id
# Trying to change symbol (will cause error)
sym3 = :bike
# sym3 [3] "cycle" # Uncommenting causes error

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

A==

B!=

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using inequality operators when equality is expected.

Trying to modify a symbol with methods like replace which do not exist.

Symbols with the same name are equal and share the same object id. Symbols cannot be changed once created, so assignment is the only way to set a symbol variable.

Practice

1.

What is a key characteristic of a Ruby Symbol?

easy

A. It is immutable and unique for the same name

B. It can be changed after creation

C. It stores large amounts of data

D. It behaves like a string with spaces

Solution

1. Step 1: Understand what a Symbol is

   A Symbol in Ruby is a name or label that is immutable, meaning it cannot be changed once created.

2. Step 2: Recognize uniqueness of Symbols

   Two Symbols with the same name always refer to the same object, making them unique and memory efficient.

3. Final Answer:

   It is immutable and unique for the same name -> Option A

4. Quick Check:

   Symbol = immutable and unique [OK]

Hint: Symbols never change and are unique by name [OK]

Common Mistakes:

• Thinking symbols can be modified like strings
• Confusing symbols with regular strings
• Assuming symbols store large data
• Believing symbols allow spaces like strings

2.

Which of the following is the correct way to write a Ruby symbol?

?

easy

A. 'my_symbol'

B. "my_symbol"

C. my_symbol

D. :my_symbol

Solution

1. Step 1: Identify symbol syntax in Ruby

   Symbols are written with a colon : followed by a name without quotes.

2. Step 2: Compare options

   Only :my_symbol uses the correct symbol syntax; others are strings or invalid.

3. Final Answer:

   :my_symbol -> Option D

4. Quick Check:

   Symbol syntax = colon + name [OK]

Hint: Symbols start with a colon : followed by name [OK]

Common Mistakes:

• Using quotes around symbols
• Writing symbols without colon
• Confusing symbols with strings
• Using invalid characters in symbol names

3.

What will be the output of the following Ruby code?

sym1 = :apple
sym2 = :apple
puts sym1.object_id == sym2.object_id

medium

A. false

B. nil

C. true

D. SyntaxError

Solution

1. Step 1: Understand symbol object identity

   Symbols with the same name share the same object_id because they are unique and immutable.

2. Step 2: Compare object_ids of sym1 and sym2

   Both :apple symbols point to the same object, so their object_ids are equal, making the comparison true.

3. Final Answer:

   true -> Option C

4. Quick Check:

   Same symbol = same object_id [OK]

Hint: Same symbol names share object_id, so comparison is true [OK]

Common Mistakes:

• Assuming different symbols have different object_ids
• Confusing symbols with strings which differ
• Expecting false because of separate variables
• Thinking symbols are mutable objects

4.

Find the error in this Ruby code snippet:

sym = :hello
sym << " world"
puts sym

medium

A. Symbols can be changed with << operator

B. Symbols cannot be concatenated with <<

C. Syntax error in symbol declaration

D. Missing quotes around symbol

Solution

1. Step 1: Check symbol mutability

   Symbols are immutable, so you cannot change them or add to them with operators like <<.

2. Step 2: Identify the error in code

   The line sym << " world" tries to modify the symbol, which causes a runtime error.

3. Final Answer:

   Symbols cannot be concatenated with << -> Option B

4. Quick Check:

   Symbols are immutable, no << allowed [OK]

Hint: Symbols cannot be changed or concatenated [OK]

Common Mistakes:

• Trying to modify symbols like strings
• Assuming symbols can be concatenated
• Confusing syntax errors with runtime errors
• Using << operator on immutable objects

5.

Given the following code, what will be the output?

hash = { apple: 1, banana: 2 }
key = :apple
hash[key] = 3
puts hash[:apple]

Consider the immutability and identity of symbols in your answer.

hard

A. 3

B. 1

C. nil

D. KeyError

Solution

1. Step 1: Understand symbol keys in hash

   Symbols used as keys are immutable and unique, so :apple and key (which is :apple) refer to the same key.

2. Step 2: Update hash value for :apple

   Assigning hash[key] = 3 updates the value for the :apple key from 1 to 3.

3. Step 3: Output the updated value

   puts hash[:apple] prints the updated value 3.

4. Final Answer:

   3 -> Option A

5. Quick Check:

   Symbol keys are unique, so value updates correctly [OK]

Hint: Symbol keys are unique; updating key changes value [OK]

Common Mistakes:

• Thinking key is different because of variable
• Expecting original value 1 instead of updated 3
• Confusing symbols with strings as keys
• Assuming symbols can be duplicated in hash keys