Everything is an object mental model in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print the class of the number 10.

Ruby

puts 10.[1]

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

Aclass

Btype

Ckind

Dobject

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'type' instead of 'class' causes an error.

In Ruby, class is the method to get the class of an object.

2fill in blank

medium

Complete the code to call the upcase method on the string 'hello'.

Ruby

puts 'hello'.[1]

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

Adowncase

Bupcase

Ccapitalize

Dreverse

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'capitalize' only changes the first letter.

The upcase method converts all letters in a string to uppercase.

3fill in blank

hard

Fix the error in the code to check if 5 is an object.

Ruby

puts 5.[1](Object)

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

Aobject?

Bis_object?

Cis_a?

Dinstance_of?

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'object?' or 'is_object?' are not valid Ruby methods.

The is_a? method checks if an object is an instance of a class or its subclass.

4fill in blank

hard

Fill both blanks to create a hash where keys are strings and values are their lengths.

Ruby

lengths = ['cat', 'dog', 'bird'].each_with_object({}) { |word, h| h[[1]] = [2] }

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

Aword

Bword.length

Cword.size

Dword.count

Attempts:

3 left

💡 Hint

Common Mistakes

Using word.size also works but is not the expected answer here.

The key is the word itself, and the value is its length using length.

5fill in blank

hard

Fill all three blanks to create a hash with uppercase keys and values greater than 3.

Ruby

result = ['apple', 'bat', 'cat', 'dog'].each_with_object({}) { |word, h| if [3]; h[[1]] = [2] end }

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

Aword.upcase

Bword

Cword.length > 3

Dword.size < 3

Attempts:

3 left

💡 Hint

Common Mistakes

Using word.size < 3 filters the wrong words.

Keys are uppercase words, values are the original words, filtered by length greater than 3.

Practice

1. In Ruby, which of the following is not considered an object?

easy

A. Numbers like 5

B. Strings like "hello"

C. Booleans like true

D. Variables themselves

Solution

1. Step 1: Understand Ruby's object model

   In Ruby, everything you work with directly, like numbers, strings, and booleans, are objects.

2. Step 2: Differentiate variables from objects

   Variables are names or references pointing to objects, but they themselves are not objects.

3. Final Answer:

   Variables themselves are not objects -> Option D

4. Quick Check:

   Variables are references, not objects [OK]

Hint: Remember: variables point to objects, they aren't objects themselves [OK]

Common Mistakes:

• Thinking variables are objects
• Confusing object instances with variable names
• Assuming booleans are not objects

2. Which of the following is the correct way to call the method upcase on a string object name in Ruby?

easy

A. name.upcase

B. upcase(name)

C. name->upcase()

D. upcase.name()

Solution

1. Step 1: Recall Ruby method call syntax

   In Ruby, methods are called on objects using dot notation: object.method.

2. Step 2: Apply to the string object

   For the string variable name, calling upcase is done as name.upcase.

3. Final Answer:

   name.upcase -> Option A

4. Quick Check:

   Method call syntax = object.method [OK]

Hint: Use dot (.) to call methods on objects in Ruby [OK]

Common Mistakes:

• Using function-style calls like upcase(name)
• Using arrow (->) notation from other languages
• Placing method after dot incorrectly

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

num = 10
puts num.class

medium

A. Integer

B. Fixnum

C. Numeric

D. Object

Solution

1. Step 1: Understand the class method

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

2. Step 2: Identify the class of the number 10 in Ruby 3.12+

   In modern Ruby versions, integers are instances of the Integer class (Fixnum and Bignum were unified).

3. Final Answer:

   Integer -> Option A

4. Quick Check:

   10.class = Integer [OK]

Hint: Use .class to find an object's type in Ruby [OK]

Common Mistakes:

• Choosing Fixnum (old Ruby versions)
• Confusing Numeric with Integer
• Thinking class returns Object always

4. The following Ruby code prints nothing. What is the problem?

text = "HELLO"
puts text.upcase!

medium

A. Missing parentheses for method call

B. Using upcase! on a string literal causes error

C. The method upcase! returns nil if no changes made

D. Strings are not objects, so methods can't be called

Solution

1. Step 1: Understand upcase! behavior

   The upcase! method modifies the string in place and returns nil if no changes were made.

2. Step 2: Analyze the code's output

   Since "HELLO" is uppercase, upcase! makes no changes and returns nil, so puts prints nothing.

3. Step 3: Identify the error cause

   The return value nil is printed when no mutation occurs.

4. Final Answer:

   upcase! returns nil if no changes made -> Option C

5. Quick Check:

   Bang methods can return nil if no change [OK]

Hint: Bang (!) methods may return nil if no change happens [OK]

Common Mistakes:

• Thinking bang methods always return a string
• Assuming strings are not objects
• Missing that upcase! modifies in place

5. Given the code below, what will be the output?

class NumberWrapper
  def initialize(value)
    @value = value
  end

  def to_s
    "Value is: #{@value.to_s}"
  end
end

num = NumberWrapper.new(42)
puts num.to_s

hard

A. 42

B. Value is: 42

C. Value is: @value

D. Error: undefined method to_s

Solution

1. Step 1: Understand the class and method definitions

   The class NumberWrapper stores a value and defines a to_s method that returns a string including the value.

2. Step 2: Analyze the to_s method call

   The method returns the string "Value is: " plus the string version of @value, which is 42.

3. Step 3: Check the output of puts num.to_s

   It prints the string returned by to_s, which is "Value is: 42".

4. Final Answer:

   Value is: 42 -> Option B

5. Quick Check:

   Custom to_s returns formatted string [OK]

Hint: to_s returns string representation of any object [OK]

Common Mistakes:

• Expecting just the number without text
• Confusing instance variable with string literal
• Thinking to_s is undefined