Implicit return (last expression) in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return the sum of two numbers without using the return keyword.

Ruby

def add(a, b)
  a [1] b
end

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

A+

B-

C/

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition.

Trying to use the return keyword explicitly.

The last expression a + b is implicitly returned by the method.

2fill in blank

medium

Complete the code to implicitly return the length of the string.

Ruby

def length_of_string(str)
  str.[1]
end

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

Asize

Bcount

Cchars

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using chars which returns an array, not a number.

Using count without arguments returns 0.

The method length returns the number of characters in the string, and since it's the last expression, it is implicitly returned.

3fill in blank

hard

Fix the error in the method to implicitly return the square of the number.

Ruby

def square(num)
  num [1] 2
end

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

A**

B*

C^

Dpow

Attempts:

3 left

💡 Hint

Common Mistakes

Using * which multiplies but does not square.

Using ^ which is a bitwise XOR, not exponentiation.

In Ruby, ** is the exponentiation operator. Using it correctly returns the square of the number implicitly.

4fill in blank

hard

Fill both blanks to create a method that returns the last character of a string implicitly.

Ruby

def last_char(str)
  str[1][2]
end

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

A[0]

B.last

C[-1]

D.first

Attempts:

3 left

💡 Hint

Common Mistakes

Using [0] or .first which return the first character.

Mixing index and method incorrectly.

Using str[-1] or str.last returns the last character. Both are valid ways to implicitly return the last character.

5fill in blank

hard

Fill all three blanks to create a method that returns a hash with keys as uppercase words and values as their lengths, implicitly.

Ruby

def word_lengths(words)
  words.each_with_object([1]) do |word, result|
    result[[2]] = word.[3]
  end
end

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

A{}

Bword.upcase

Clength

D[]

Attempts:

3 left

💡 Hint

Common Mistakes

Using square brackets [] instead of an empty hash {}.

Using word instead of word.upcase as keys.

Using size or other methods instead of length.

The method uses each_with_object({}) to build a hash. The key is the uppercase word word.upcase, and the value is the length of the word word.length. The last expression is implicitly returned.

Practice

1. What does Ruby return from a method if there is no explicit return statement?

easy

A. The value of the last expression evaluated in the method

B. Always nil

C. The first expression evaluated in the method

D. An error occurs

Solution

1. Step 1: Understand Ruby method return behavior

   Ruby methods automatically return the value of the last expression evaluated if no explicit return is used.

2. Step 2: Apply this to the question

   Since no explicit return is given, the method returns the last expression's value.

3. Final Answer:

   The value of the last expression evaluated in the method -> Option A

4. Quick Check:

   Implicit return = last expression value [OK]

Hint: Remember: Ruby returns last expression automatically [OK]

Common Mistakes:

• Thinking Ruby returns nil by default
• Assuming explicit return is always needed
• Confusing first and last expression return

2. Which of the following Ruby method definitions correctly uses implicit return?

easy

A. def add(a, b)
a + b
end

B. def add(a, b)
return a + b
puts 'done'
end

C. def add(a, b)
puts a + b
end

D. def add(a, b)
a + b; return
end

Solution

1. Step 1: Check each method for implicit return usage

   def add(a, b) a + b end returns the last expression a + b implicitly without return.

2. Step 2: Analyze other options

   def add(a, b) return a + b puts 'done' end uses explicit return, def add(a, b) puts a + b end returns nil because puts returns nil, def add(a, b) a + b; return end has return with no value, returning nil.

3. Final Answer:

   def add(a, b) a + b end -> Option A

4. Quick Check:

   Implicit return = last expression value [OK]

Hint: Implicit return means last line's value is returned [OK]

Common Mistakes:

• Confusing puts output with return value
• Using return unnecessarily
• Returning nil unintentionally

3. What is the output of this Ruby code?

def greet(name)
  message = "Hello, "+name
  message.upcase
end

puts greet("Alice")

medium

A. "Hello, Alice"

B. Error

C. nil

D. "HELLO, ALICE"

Solution

1. Step 1: Trace method execution

   The method creates message as "Hello, Alice" then calls message.upcase which returns "HELLO, ALICE".

2. Step 2: Determine return value

   Since message.upcase is the last expression, it is implicitly returned.

3. Final Answer:

   "HELLO, ALICE" -> Option D

4. Quick Check:

   Last expression returned = "HELLO, ALICE" [OK]

Hint: Last expression value is returned automatically [OK]

Common Mistakes:

• Assuming original message is returned
• Thinking puts output is return value
• Confusing method return with print output

4. Identify the error in this Ruby method related to implicit return:

def multiply(x, y)
  product = x * y
  puts product
end

result = multiply(3, 4)
puts result

medium

A. Method returns product correctly

B. Syntax error due to missing return

C. Method returns nil because last expression is puts

D. Method raises runtime error

Solution

1. Step 1: Analyze last expression in method

   The last expression is puts product, which returns nil.

2. Step 2: Understand method return value

   Because Ruby returns the last expression implicitly, the method returns nil, not the product.

3. Final Answer:

   Method returns nil because last expression is puts -> Option C

4. Quick Check:

   Implicit return = last expression value (puts returns nil) [OK]

Hint: puts returns nil, so method returns nil if last line is puts [OK]

Common Mistakes:

• Expecting method to return printed value
• Thinking missing return causes syntax error
• Confusing output with return value

5. Given this method, what will be the return value?

def check_value(val)
  if val > 10
    "High"
  else
    "Low"
  end
end

check_value(10)

hard

A. "High"

B. "Low"

C. nil

D. Error

Solution

1. Step 1: Evaluate the condition with val = 10

   Since 10 is not greater than 10, the else branch executes returning "Low".

2. Step 2: Understand implicit return in if-else

   The last evaluated expression is the string "Low", which is implicitly returned by the method.

3. Final Answer:

   "Low" -> Option B

4. Quick Check:

   Implicit return of last expression in if-else = "Low" [OK]

Hint: If-else returns last expression evaluated implicitly [OK]

Common Mistakes:

• Assuming val > 10 includes 10
• Expecting explicit return needed
• Confusing nil with else return