Ruby - Handle NoMethodError by Using begin-rescue-end

1. Introduction

In Ruby, when we try to call a method that doesn't exist for an object, it raises a NoMethodError. This error can sometimes interrupt the flow of an application. However, Ruby provides a mechanism to handle exceptions gracefully using the begin-rescue-end construct. In this post, we'll explore how to handle the NoMethodError exception using this construct.

NoMethodError is an exception raised in Ruby when an undefined method is invoked on an object. This typically indicates that the method doesn't exist for that particular object or hasn't been defined yet.

2. Program Steps

1. Define an object or use an existing one.

2. Within the begin...rescue block, attempt to call a method that doesn't exist for that object.

3. If a NoMethodError exception is encountered, handle it gracefully by displaying a custom error message.

4. If no exception is encountered, the method call will execute as expected.

3. Code Program

# Define a sample array
sample_array = [1, 2, 3]
# Attempt to call an undefined method within a begin...rescue block
begin
  sample_array.undefined_method
rescue NoMethodError
  puts "Error: The method you are trying to call does not exist!"
end

Output:

Error: The method you are trying to call does not exist!

Explanation:

1. sample_array = [1, 2, 3]: Here we define a simple array.

2. begin: This starts the begin...rescue block where we will attempt to call the undefined method.

3. sample_array.undefined_method: This line tries to call an undefined_method on the sample_array which doesn't exist, leading to a NoMethodError.

4. rescue NoMethodError: This line catches the NoMethodError exception when raised.

5. puts "Error: The method you are trying to call does not exist!": This line displays a custom error message when the NoMethodError exception is encountered.