Type checking with .class and .is_a? in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the variable is exactly an Integer using .class.

Ruby

num = 10
puts num.class == [1]

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

AFixnum

BInteger

CNumber

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'int' or 'Fixnum' which are not valid class names in modern Ruby.

The .class method returns the exact class of an object. To check if num is an Integer, compare num.class with Integer.

2fill in blank

medium

Complete the code to check if the variable is a kind of Numeric using .is_a?.

Ruby

value = 3.14
puts value.[1](Numeric)

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

Akind_of?

Binstance_of?

Cis_a?

Dclass_of?

Attempts:

3 left

💡 Hint

Common Mistakes

Using instance_of? which checks only exact class, not subclasses.

The .is_a? method checks if an object is an instance of a class or its subclass. Here, it checks if value is a kind of Numeric.

3fill in blank

hard

Fix the error in the code to correctly check if 'text' is a String using .class.

Ruby

text = "hello"
if text.class [1] String
  puts "It's a string!"
end

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

AString

Bequals

Cis_a?

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using single equals = instead of double equals == for comparison.

The code uses a single equals sign = which is assignment, not comparison. To compare classes, use ==.

4fill in blank

hard

Fill both blanks to create a hash of words and their lengths, including only words longer than 3 characters.

Ruby

words = ["cat", "house", "dog", "elephant"]
lengths = {word: word.[1] for word in words if word.[1] [2] 3}

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

Alength

Bsize

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using word.length is valid but not in options; using < instead of >.

Use word.size to get the length of the word. The condition word > 3 is invalid, so use word.size > 3 to filter words longer than 3 characters.

5fill in blank

hard

Fill all three blanks to create a hash with uppercase words as keys and their lengths as values, including only words with length greater than 4.

Ruby

words = ["apple", "bat", "carrot", "dog"]
result = { [1]: [2] for w in words if [2] [3] 4 }

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

Aw.upcase

Bw.length

C>

Dw.downcase

Attempts:

3 left

💡 Hint

Common Mistakes

Using w.downcase instead of w.upcase for keys; using < instead of >.

Use w.upcase for keys to get uppercase words, w.length for values to get word length, and > to filter words longer than 4 characters.

Practice

1. What does the .class method return when called on an object in Ruby?

easy

A. Whether the object is a kind of a class

B. The exact type (class) of the object

C. The parent class of the object

D. A boolean indicating if the object is a class

Solution

1. Step 1: Understand what .class does

   The .class method returns the exact class of the object it is called on.

2. Step 2: Compare with other options

   Options A, C, and D describe behaviors of other methods or incorrect meanings.

3. Final Answer:

   The exact type (class) of the object -> Option B

4. Quick Check:

   .class returns exact type [OK]

Hint: Remember: .class gives exact type, not inheritance [OK]

Common Mistakes:

• Confusing .class with .is_a?
• Thinking .class returns boolean
• Assuming .class returns parent class

2. Which of the following is the correct syntax to check if variable x is an instance of the Integer class using .is_a??

easy

A. x.is_a?(Integer)

B. x.is_a(Integer)

C. x.is_a<Integer>

D. x.is_a? Integer

Solution

1. Step 1: Recall the syntax of .is_a?

   The method .is_a? requires a class argument inside parentheses, like .is_a?(ClassName).

2. Step 2: Check each option

   x.is_a?(Integer) uses correct syntax with parentheses and question mark. Options A, B, and D have syntax errors or missing parentheses.

3. Final Answer:

   x.is_a?(Integer) -> Option A

4. Quick Check:

   Use parentheses with .is_a? [OK]

Hint: Always use parentheses with .is_a? method [OK]

Common Mistakes:

• Omitting parentheses after .is_a?
• Using angle brackets instead of parentheses
• Leaving out the question mark

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

class Animal; end
class Dog < Animal; end

dog = Dog.new
puts dog.class
puts dog.is_a?(Animal)

medium

A. Dog
true

B. Animal
true

C. Dog
false

D. Animal
false

Solution

1. Step 1: Understand dog.class

   The dog object is an instance of Dog, so dog.class returns Dog.

2. Step 2: Understand dog.is_a?(Animal)

   Since Dog inherits from Animal, dog.is_a?(Animal) returns true.

3. Final Answer:

   Dog true -> Option A

4. Quick Check:

   .class exact type, .is_a? checks inheritance [OK]

Hint: Remember: .class exact, .is_a? true for subclasses too [OK]

Common Mistakes:

• Thinking .class returns parent class
• Assuming .is_a? false for subclasses
• Confusing output order

4. Identify the error in the following Ruby code snippet:

num = 10
if num.is_a?(Integer)
  puts "Number is integer"
else
  puts "Number is not integer"
end

medium

A. Syntax error in if statement

B. Missing parentheses in is_a? call

C. No error, code runs correctly

D. Incorrect class name Integer

Solution

1. Step 1: Check is_a? usage

   The method .is_a? is correctly called with parentheses and the class Integer.

2. Step 2: Verify syntax correctness

   The if statement and puts calls are syntactically correct.

3. Final Answer:

   No error, code runs correctly -> Option C

4. Quick Check:

   Correct syntax and usage means no error [OK]

Hint: Check parentheses and class names carefully [OK]

Common Mistakes:

• Removing parentheses from is_a?
• Using wrong class name like 'int'
• Misplacing if-end keywords

5. Given the following code, which option correctly filters only strings from the mixed array using .is_a??

items = ["apple", 42, :symbol, "banana", 3.14]
strings = items.select { |item| ??? }

hard

A. item.class != String

B. item.class == String

C. item.is_a?(Integer)

D. item.is_a?(String)

Solution

1. Step 1: Understand filtering with .is_a?

   We want to select only elements that are strings, so we check if each item is a kind of String.

2. Step 2: Compare options

   item.is_a?(String) uses .is_a?(String) which returns true for strings. item.class == String uses .class == String which also works but is less flexible if subclasses exist. Options C and D filter integers or non-strings, which is incorrect.

3. Final Answer:

   item.is_a?(String) -> Option D

4. Quick Check:

   Use .is_a?(String) to filter strings [OK]

Hint: Use .is_a?(String) to include subclasses too [OK]

Common Mistakes:

• Using .class == String and missing subclasses
• Filtering wrong types by mistake
• Forgetting question mark in .is_a?