Prepend for method chain insertion in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the prepend method do in Ruby?

It inserts a module before the current class in the method lookup chain, so methods in the prepended module override the class's own methods.

intermediate

How is prepend different from include in Ruby?

<code>include</code> adds a module after the class in the method lookup chain, so class methods override module methods. <code>prepend</code> adds the module before the class, so module methods override class methods.

intermediate

Why use prepend for method chain insertion?

Because it lets you insert behavior before existing methods without changing the original class, enabling method wrapping or overriding cleanly.

beginner

Given this code:<br><pre>module M
  def greet
    "Hello from M"
  end
end

class C
  def greet
    "Hello from C"
  end
end

c = C.new
puts c.greet</pre><br>What will <code>c.greet</code> print after <code>C.prepend(M)</code>?

It will print "Hello from M" because prepend puts module M before class C in the method lookup chain.

intermediate

How can you call the original method from a prepended module's method?

Use <code>super</code> inside the prepended module's method to call the original method defined in the class or other modules further down the chain.

What happens when you use prepend with a module in Ruby?

A The class's methods override the module's methods.

B The module's methods are ignored.

C The module's methods override the class's methods.

D The module is added after the class in the lookup chain.

prepend inserts the module before the class in the method lookup chain, so the module's methods override the class's methods.

Which keyword lets you call the original method from inside a prepended module's method?

A base

B this

C self

D super

super calls the next method in the lookup chain, allowing access to the original method.

If a module is included instead of prepended, which methods take precedence?

A Class methods override module methods.

B Module methods and class methods have equal precedence.

C Module methods override class methods.

D Neither methods are called.

include adds the module after the class, so class methods override module methods.

Why might you use prepend instead of reopening a class to override a method?

A Because <code>prepend</code> is slower.

B To avoid changing the original class directly and keep code modular.

C Because <code>prepend</code> disables method overriding.

D To remove methods from the class.

prepend allows inserting behavior cleanly without modifying the original class code.

What will this code output?<br>

module M
  def hello
    "Hi from M" + super
  end
end

class C
  def hello
    "Hi from C"
  end
end

C.prepend(M)
puts C.new.hello

A Hi from MHi from C

B Error

C Hi from M

D Hi from C

The prepended module's hello calls super, which calls the class's hello, so the output concatenates both strings.

Explain how prepend changes the method lookup chain in Ruby and why that is useful for method chain insertion.

Think about where the module sits compared to the class in the search for methods.

Describe how you can use super inside a prepended module's method to extend behavior rather than replace it.

How do you keep the original method's effect while adding new behavior?