How to Fix Undefined Method in Ruby

This article will discuss fixing the most common error in Ruby projects, the undefined method.

Fix Undefined Method in Ruby

The undefined method is also called the NoMethodError exception, and it’s the most common error within projects, according to The 2022 Airbrake Error Data Report.

It occurs when a receiver (an object) receives a method that does not exist.

Undefined Method on an Inbuilt Object

The code below demonstrates how to trigger a NoMethodError error on an array object if we call an undefined method maximum on it.

Example code:

arr = [1, 2, 3, 7, 4]
puts arr.maximum

Output:

undefined method `maximum' for [1, 2, 3, 7, 4]:Array (NoMethodError)

Undefined Method on a Custom Object

The code below demonstrates how to trigger a NoMethodError error on a custom object.

Example code:

class Employee
  def initialize(last_name, first_name)
    @last_name = last_name
    @first_name = first_name
  end

  def full_name
    "#{@first_name} #{@last_name}"
  end
end

employee1 = Employee.new('John', 'Doe')
puts employee1.fullname

Output:

undefined method `fullname' for #<Employee:0x0000565026778608> (NoMethodError)
Did you mean? full_name

In the example above, we intentionally used fullname instead of full_name, and as a result, Ruby could not find a match but found a name that looked very close. Hence, Did you mean? full_name was added to the error traceback.