Prepend for method chain insertion in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to prepend a string to another string.

Ruby

result = 'world'.[1]('Hello ')
puts result

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

Aprepend

Bappend

Cinsert

Dconcat

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'append' which adds text at the end.

Using 'concat' which also adds at the end.

The prepend method adds the given string to the beginning of the original string.

2fill in blank

medium

Complete the code to prepend 'Mr. ' to the name variable.

Ruby

name = 'Smith'
name.[1]('Mr. ')
puts name

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

Aconcat

Bprepend

Cinsert

Dappend

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'append' which adds text at the end.

Using 'insert' with wrong index.

Using prepend adds 'Mr. ' at the start of the string stored in name.

3fill in blank

hard

Fix the error in the code to prepend 'Hello, ' to the greeting string.

Ruby

greeting = 'world'
greeting.[1]('Hello, ')
puts greeting

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

Aappend

Bconcat

Cprepend

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'append' which adds text at the end.

Using 'concat' which adds at the end.

The prepend method modifies the string by adding the argument at the start. It returns the modified string, so assignment is optional but allowed.

4fill in blank

hard

Fill both blanks to prepend 'Hello, ' and then append '!' to the string.

Ruby

text = 'world'
text.[1]('Hello, ').[2]('!')
puts text

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

Aprepend

Bappend

Cconcat

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'append' first which adds at the end before prepending.

Using 'concat' instead of 'append'.

First, prepend adds 'Hello, ' at the start. Then, append adds '!' at the end.

5fill in blank

hard

Fill all three blanks to prepend 'Hello, ', convert to uppercase, and then append '!' to the string.

Ruby

text = 'world'
text = text.[1]('Hello, ').[2].[3]('!')
puts text

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

Aprepend

Bupcase

Cappend

Ddowncase

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'downcase' instead of 'upcase'.

Appending before prepending.

First, prepend adds 'Hello, ' at the start. Then upcase converts the whole string to uppercase. Finally, append adds '!' at the end.

Practice

1. What does the prepend keyword do in Ruby when used with a module and a class?

easy

A. It inserts the module before the class in the method lookup chain.

B. It appends the module after the class in the method lookup chain.

C. It replaces the class methods with the module methods permanently.

D. It creates a copy of the module inside the class without affecting method lookup.

Solution

1. Step 1: Understand method lookup order with prepend

   Using prepend places the module before the class in the method lookup chain, so module methods are checked first.

2. Step 2: Compare prepend with other module inclusion methods

   Unlike include which adds the module after the class, prepend inserts it before, changing method resolution order.

3. Final Answer:

   It inserts the module before the class in the method lookup chain. -> Option A

4. Quick Check:

   Prepend = module methods run first [OK]

Hint: Prepend means module methods run before class methods [OK]

Common Mistakes:

• Confusing prepend with include
• Thinking prepend replaces class methods permanently
• Assuming prepend appends module after class

2. Which of the following is the correct syntax to prepend a module Mod to a class MyClass?

easy

A. class MyClass; extend Mod; end

B. class MyClass; include Mod; end

C. class MyClass; prepend Mod; end

D. class MyClass; insert Mod; end

Solution

1. Step 1: Recall Ruby syntax for prepend

   The correct syntax to prepend a module is prepend ModuleName inside the class definition.

2. Step 2: Eliminate other options

   include adds module after class, extend adds methods as class methods, and insert is invalid syntax.

3. Final Answer:

   class MyClass; prepend Mod; end -> Option C

4. Quick Check:

   Prepend syntax = prepend ModuleName [OK]

Hint: Use 'prepend ModuleName' inside class to insert module first [OK]

Common Mistakes:

• Using include instead of prepend
• Using extend which affects class methods
• Typing invalid keywords like insert

3. What is the output of this Ruby code?

module M
  def greet
    "Hello from M, " + super
  end
end

class C
  prepend M
  def greet
    "Hello from C"
  end
end

puts C.new.greet

medium

A. "Hello from C"

B. "Hello from M, Hello from C"

C. NoMethodError

D. "Hello from M"

Solution

1. Step 1: Understand method lookup with prepend

   Because M is prepended, its greet method is called first.

2. Step 2: Follow the super call in module method

   The super inside M#greet calls the original greet in C, returning "Hello from C".

3. Step 3: Combine returned strings

   The module method returns "Hello from M, " + "Hello from C" resulting in "Hello from M, Hello from C".

4. Final Answer:

   "Hello from M, Hello from C" -> Option B

5. Quick Check:

   Prepend + super calls original method [OK]

Hint: Prepend runs module method first; super calls original method [OK]

Common Mistakes:

• Ignoring super call and expecting only module output
• Thinking prepend replaces original method without super
• Expecting NoMethodError due to super

4. Identify the error in this Ruby code using prepend:

module M
  def hello
    super + " world"
  end
end

class C
  prepend M
end

puts C.new.hello

medium

A. TypeError because prepend is used incorrectly

B. No error; outputs " world"

C. SyntaxError due to missing method in class

D. NoMethodError because super has no method to call

Solution

1. Step 1: Check method definitions

   The module M defines hello calling super, but class C has no hello method.

2. Step 2: Understand super call behavior

   Since C has no hello, super has no method to call, causing a NoMethodError.

3. Final Answer:

   NoMethodError because super has no method to call -> Option D

4. Quick Check:

   Super needs original method; missing causes NoMethodError [OK]

Hint: Super must call existing method; else NoMethodError [OK]

Common Mistakes:

• Assuming super works without original method
• Thinking prepend fixes missing methods automatically
• Confusing syntax error with runtime error

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

module A
  def info
    "A" + super
  end
end

module B
  def info
    "B" + super
  end
end

class Base
  def info
    "Base"
  end
end

class MyClass < Base
  prepend A
  prepend B
end

puts MyClass.new.info

hard

A. "BABase"

B. "BaseAB"

C. "ABBase"

D. "BASuperBase"

Solution

1. Step 1: Understand multiple prepends order

   Modules prepended last are checked first, so B is before A in lookup.

2. Step 2: Trace method calls

   B#info runs first, returns "B" + super, which calls A#info, returning "A" + super, which calls Base#info returning "Base".

3. Step 3: Combine results

   Concatenate strings: "B" + "A" + "Base" = "BABase".

4. Final Answer:

   "BABase" -> Option A

5. Quick Check:

   Last prepend runs first; super chains down [OK]

Hint: Last prepended module runs first in method chain [OK]

Common Mistakes:

• Assuming first prepended module runs first
• Ignoring method lookup order with multiple prepends
• Confusing prepend with include order