Immutable data with freeze in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to freeze the string so it cannot be changed.

Ruby

name = "Ruby".[1]
name << "Lang"

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

Aupcase

Bfreeze

Creverse

Dcapitalize

Attempts:

3 left

💡 Hint

Common Mistakes

Using string methods that modify content instead of freezing.

Not calling any method and expecting immutability.

Using freeze makes the string immutable, so appending to it causes an error.

2fill in blank

medium

Complete the code to freeze the array so it cannot be modified.

Ruby

numbers = [1, 2, 3].[1]
numbers << 4

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

Areverse

Bsort

Cfreeze

Duniq

Attempts:

3 left

💡 Hint

Common Mistakes

Using sorting or reversing methods instead of freezing.

Trying to modify without freezing first.

Calling freeze on the array prevents adding new elements.

3fill in blank

hard

Fix the error by freezing the hash so it cannot be changed.

Ruby

config = {mode: 'dark', volume: 10}
config.[1]
config[:mode] = 'light'

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

Afreeze

Bdelete

Cdup

Dclear

Attempts:

3 left

💡 Hint

Common Mistakes

Using methods that remove or copy instead of freezing.

Not freezing before trying to modify.

Freezing the hash prevents changing its keys or values.

4fill in blank

hard

Fill both blanks to create a frozen array and check if it is frozen.

Ruby

arr = [10, 20, 30].[1]
puts arr.[2]

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

Afreeze

Bfrozen?

Cempty?

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using empty? or length instead of frozen?.

Not freezing the array before checking.

First, freeze the array to make it immutable, then check with frozen?.

5fill in blank

hard

Fill all three blanks to freeze a nested hash and check if the nested array is frozen.

Ruby

settings = {theme: 'blue', options: [1, 2, 3]}
settings = settings.[1]
puts settings[:options].[2]
settings[:options].[3]

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

Afreeze

Bfrozen?

Ddup

Attempts:

3 left

💡 Hint

Common Mistakes

Assuming freezing outer hash freezes nested objects.

Not freezing nested array separately.

Freeze the outer hash, check if the nested array is frozen (it is not), then freeze the nested array separately to make it immutable.

Practice

1. What does the freeze method do to an object in Ruby?

easy

A. Prevents any further modifications to the object

B. Deletes the object from memory

C. Duplicates the object

D. Makes the object mutable

Solution

1. Step 1: Understand the purpose of freeze

   The freeze method is used to make an object immutable, meaning it cannot be changed after freezing.

2. Step 2: Identify the effect on the object

   Once frozen, any attempt to modify the object will raise an error, so it prevents further changes.

3. Final Answer:

   Prevents any further modifications to the object -> Option A

4. Quick Check:

   freeze makes object immutable = Prevents changes [OK]

Hint: Freeze means no changes allowed after calling it [OK]

Common Mistakes:

• Thinking freeze deletes the object
• Confusing freeze with duplication
• Assuming freeze makes object mutable

2. Which of the following is the correct way to freeze a string name in Ruby?

easy

A. freeze(name)

B. name.frozen = true

C. name.freeze()

D. freeze name

Solution

1. Step 1: Recall Ruby method call syntax

   In Ruby, to call a method on an object, use dot notation like object.method().

2. Step 2: Identify the correct freeze syntax

   The correct way to freeze the string name is name.freeze(). Other options are invalid syntax or incorrect usage.

3. Final Answer:

   name.freeze() -> Option C

4. Quick Check:

   Method call with dot and parentheses = Correct freeze syntax [OK]

Hint: Use dot notation: object.freeze() to freeze [OK]

Common Mistakes:

• Using freeze as a standalone function
• Trying to assign frozen = true
• Omitting dot before freeze

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

arr = [1, 2, 3]
arr.freeze
arr << 4
puts arr.inspect

medium

A. [1, 2, 3, 4]

B. RuntimeError: can't modify frozen Array

C. [1, 2, 3]

D. SyntaxError

Solution

1. Step 1: Understand freezing the array

   The array arr is frozen using arr.freeze, making it immutable.

2. Step 2: Analyze the modification attempt

   Trying to append 4 with arr << 4 will raise a RuntimeError because the array is frozen and cannot be changed.

3. Final Answer:

   RuntimeError: can't modify frozen Array -> Option B

4. Quick Check:

   Frozen object + modification = RuntimeError [OK]

Hint: Modifying frozen object causes RuntimeError [OK]

Common Mistakes:

• Assuming frozen array can still be changed
• Expecting silent failure or no error
• Confusing output with syntax error

4. Identify the error in this Ruby code snippet:

str = "hello"
str.freeze
str[0] = 'H'
puts str

medium

A. RuntimeError: can't modify frozen String

B. SyntaxError due to invalid string modification

C. No error, output is "Hello"

D. Output is "hello" without changes

Solution

1. Step 1: Recognize string freezing effect

   The string str is frozen, so it cannot be changed after str.freeze.

2. Step 2: Understand the attempted modification

   Trying to change the first character with str[0] = 'H' raises a RuntimeError because the string is frozen.

3. Final Answer:

   RuntimeError: can't modify frozen String -> Option A

4. Quick Check:

   Frozen string + modification = RuntimeError [OK]

Hint: Frozen string cannot be changed, causes RuntimeError [OK]

Common Mistakes:

• Thinking string changes silently fail
• Expecting output "Hello" without error
• Confusing syntax error with runtime error

5. Given this code, what is the best way to safely modify a frozen array without error?

original = [10, 20, 30].freeze
# Your code here to add 40

hard

A. original.freeze(false)

B. original << 40

C. original.push(40)

D. original = original.dup << 40

Solution

1. Step 1: Understand frozen array cannot be changed

   The array original is frozen, so direct modification like << or push will cause errors.

2. Step 2: Use duplication to create a modifiable copy

   Using original.dup creates a new unfrozen copy. Then appending 40 to this copy is allowed.

3. Step 3: Assign the modified copy back

   Assigning the new array with 40 added back to original variable safely updates it without error.

4. Final Answer:

   original = original.dup << 40 -> Option D

5. Quick Check:

   Duplicate frozen object before modifying = Safe change [OK]

Hint: Duplicate frozen object before changing it [OK]

Common Mistakes:

• Trying to modify frozen array directly
• Using non-existent freeze(false) method
• Assuming push works on frozen array