Define_method for dynamic methods in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does define_method do in Ruby?

<p><code>define_method</code> creates a new method dynamically at runtime. It lets you define a method with a given name and block of code inside a class or module.</p>

beginner

How do you use define_method to create a method named greet that prints 'Hello'?

define_method(:greet) do
  puts 'Hello'
end

intermediate

Why use define_method instead of regular method definitions?

It helps when you want to create many similar methods dynamically, or when method names depend on data available only at runtime.

intermediate

Can define_method access variables from the surrounding scope?

Yes, the block passed to define_method can use variables from the surrounding scope because it is a closure.

intermediate

What is a simple example of using define_method to create multiple methods in a loop?

[:one, :two, :three].each do |name|
  define_method(name) do
    puts "Method #{name} called"
  end
end

What argument does define_method take first?

A The class name

B The method body as a string

C The method visibility

D The method name as a symbol or string

define_method first takes the method name as a symbol or string, then a block defining the method body.

Which of these is true about methods created with define_method?

A They can only be private methods

B They can access variables from the surrounding scope

C They cannot take arguments

D They must be defined outside classes

Methods created with define_method can access variables from the surrounding scope because the block is a closure.

Why might you use define_method inside a loop?

A To change method visibility

B To delete existing methods

C To create multiple methods with similar behavior but different names

D To call methods automatically

Using define_method inside a loop lets you create many methods with different names but similar code easily.

What happens if you call define_method with a method name that already exists?

A It overwrites the existing method

B It raises an error

C It ignores the new definition

D It creates a method with a different name

define_method will overwrite the existing method with the new definition.

Which Ruby feature allows define_method blocks to remember variables from outside?

A Closures

B Inheritance

C Modules

D Singleton methods

Closures let blocks remember variables from the surrounding scope, which define_method uses.

Explain how define_method can be used to create methods dynamically in Ruby.

Think about how you can create methods when you don't know their names before running the program.

Describe a scenario where using define_method is better than writing methods normally.

Imagine you want to create methods based on a list of names or actions.