Dynamic Method Definition
Learn how to define and call methods dynamically using define_method and method_missing.
Dynamic Method Definition is a free Ruby Academy lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Ruby Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
1
Dynamic Method Definition
In Ruby, methods can be created dynamically at runtime.
This allows for more flexible and reusable code.
2
Using define_method
The define_method method allows defining methods dynamically.
class Person
define_method(:greet) { puts 'Hello!' }
end
p = Person.new
p.greet3
Using define_method with Parameters
You can pass arguments to dynamically created methods.
class Person
define_method(:greet) { |name| puts "Hello, #{name}!" }
end
p = Person.new
p.greet('Alice')4
Using method_missing
The method_missing method intercepts calls to undefined methods.
class Person
def method_missing(name, *args)
puts "Method '#{name}' is missing!"
end
end
p = Person.new
p.unknown_method5
Handling method_missing Dynamically
You can use method_missing to define flexible method handling.
class DynamicPerson
def method_missing(name, *args)
if name.to_s.start_with?('say_')
puts "You asked me to say: #{name.to_s.split('_')[1..-1].join(' ')}"
else
super
end
end
end
p = DynamicPerson.new
p.say_hello_world6
Overriding respond_to_missing?
To properly handle method checks, override respond_to_missing?.
class DynamicPerson
def method_missing(name, *args)
if name.to_s.start_with?('say_')
puts "Saying: #{name.to_s.split('_')[1..-1].join(' ')}"
else
super
end
end
def respond_to_missing?(name, include_private = false)
name.to_s.start_with?('say_') || super
end
end
p = DynamicPerson.new
puts p.respond_to?(:say_hello)7
Using method_missing for Dynamic Getters and Setters
You can create dynamic attributes using method_missing.
class DynamicPerson
def initialize
@data = {}
end
def method_missing(name, *args)
attribute = name.to_s.sub(/=$/, '')
if name.to_s.end_with?('=')
@data[attribute] = args.first
else
@data[attribute]
end
end
end
p = DynamicPerson.new
p.name = 'Alice'
puts p.name8
9
Security Risks of method_missing
Using method_missing improperly can introduce risks:
- Unexpected behavior when handling unknown methods.
- Potential performance issues due to excessive method lookups.
- Security vulnerabilities if combined with user input.
10
Congratulations!
You have learned how to define and call methods dynamically in Ruby.
Next, you will explore open classes and monkey patching.
Frequently asked questions
Is the “Dynamic Method Definition” lesson free?
Yes — the full text of “Dynamic Method Definition” is free to read here on the web, and the Ruby Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Ruby Academy course, upgrade to CoddyKit PRO.
What will I learn in “Dynamic Method Definition”?
Learn how to define and call methods dynamically using define_method and method_missing. You practise Ruby Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Ruby Academy?
No prior experience is required. Ruby Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Dynamic Method Definition” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Ruby Academy lesson?
Yes. Every Ruby Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- What is Metaprogramming?
- Dynamic Method Definition
- Open Classes and Monkey Patching
- Using send and eval