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What are Errors in Ruby?

In this blog post, we will discuss a fundamental concept in programming, especially in Ruby: errors. If you're learning programming, you've most likely come across errors in your code, and sometimes they can be frustrating. But don't worry! Errors are a natural part of the programming process, and they often provide valuable feedback to help us improve our code.

We'll try to keep jargon to a minimum, but if we do use some technical terms, we'll make sure to explain them. Let's dive in!

What are Errors?

Errors, in the context of programming, are events that occur when a program encounters an issue that prevents it from executing correctly. These issues can stem from various reasons, such as syntax mistakes, incorrect use of functions or libraries, or even runtime conditions that the program did not anticipate.

Errors in Ruby can be broadly classified into two categories:

Syntax Errors: These occur when the code you've written does not follow the rules of the Ruby language. The Ruby interpreter cannot understand the code and, as a result, cannot execute it. Syntax errors are usually easy to fix once you identify them.

Exceptions: These are errors that occur during the execution of a program. Exceptions can happen for various reasons, such as trying to access a non-existent file or dividing a number by zero. Ruby has a built-in system for handling exceptions, which we will explore later in this post.

Syntax Errors

Let's start with syntax errors. As mentioned earlier, syntax errors occur when your code does not follow the rules of the Ruby language. Here's an example of a syntax error:

puts "Hello, World!

In this example, we forget to close the double quotes for the string. The Ruby interpreter will throw a syntax error, as it expects the string to be closed:

syntax error, unexpected end-of-input, expecting `)'

To fix this error, we simply need to close the double quotes:

puts "Hello, World!"

Common Syntax Errors

Here are some common syntax errors you might encounter when coding in Ruby:

  1. Mismatched brackets, braces, or parentheses: Make sure that you close any open brackets, braces, or parentheses. For example, the following code has mismatched parentheses:

ruby if (x > 10 puts "x is greater than 10" end

To fix this, close the parentheses:

ruby if (x > 10) puts "x is greater than 10" end

  1. Incorrect use of keywords: Ruby has reserved keywords that should not be used for variable or method names. For example, the following code uses the keyword end as a variable name, which is not allowed:

ruby end = 5

To fix this, change the variable name to something else:

ruby finish = 5

  1. Missing or extra commas: When working with arrays or hashes, make sure you separate the elements with commas. Missing or extra commas can result in syntax errors. For example, the following code has a missing comma:

ruby my_array = [1, 2 3]

To fix this, add the missing comma:

ruby my_array = [1, 2, 3]


Now that we've discussed syntax errors, let's move on to exceptions. Exceptions are errors that occur during the execution of a program. When an exception occurs, Ruby will stop executing the current block of code and look for instructions on how to handle the exception.

Handling Exceptions

Ruby has a built-in system for handling exceptions called begin-rescue-end. When you wrap your code in a begin-rescue block, you're telling Ruby to try to execute the code in the begin block. If an exception occurs, Ruby will stop executing the begin block and move on to the rescue block, where you can specify what to do in case of an exception.

Here's an example of using begin-rescue to handle an exception:

  # Code that might raise an exception
  result = 10 / 0
  # Code to execute if an exception occurs
  puts "An error occurred!"
  result = nil

puts "Result: #{result}"

In this example, we try to divide 10 by 0, which will raise a ZeroDivisionError exception. Since we've wrapped our code in a begin-rescue block, Ruby will execute the rescue block when the exception occurs. In this case, we're printing an error message and setting the result variable to nil.

Common Exceptions

Here are some common exceptions you might encounter when coding in Ruby:

  1. ZeroDivisionError: This exception is raised when you try to divide a number by zero. To fix this, ensure that the divisor is not zero or handle the exception using a begin-rescue block.


ruby begin result = 10 / 0 rescue ZeroDivisionError puts "Cannot divide by zero" result = nil end

  1. NoMethodError: This exception is raised when you try to call a method that does not exist on an object. To fix this, check your method names and ensure that the method is defined on the object you are calling it on.


```ruby class MyClass end

my_object = begin my_object.non_existent_method rescue NoMethodError puts "The method does not exist" end ```

  1. NameError: This exception is raised when you try to use a variable or method that has not been defined. To fix this, check your variable and method names and ensure that they are defined before you use them.


ruby begin puts non_existent_variable rescue NameError puts "The variable does not exist" end

Custom Exceptions

In addition to Ruby's built-in exceptions, you can also define your own custom exceptions. Custom exceptions are useful when you want to provide more specific information about the error that occurred.

To define a custom exception, create a new class that inherits from the StandardError class. For example, let's create a custom exception called InsufficientFundsError:

class InsufficientFundsError < StandardError
  attr_reader :balance, :amount

  def initialize(balance, amount)
    @balance = balance
    @amount = amount
    super("Insufficient funds: balance #{balance}, amount #{amount}")

Now, you can raise this custom exception in your code like this:

def withdraw_money(balance, amount)
  raise, amount) if balance < amount
  balance - amount

  balance = 100
  amount = 150
  new_balance = withdraw_money(balance, amount)
rescue InsufficientFundsError => e
  puts e.message

In this example, if the balance is less than the amount, we raise an InsufficientFundsError exception. We then use a begin-rescue block to handle the exception and print out a custom error message.


Errors are an inevitable part of programming, but understanding and handling them effectively can improve your code quality and make your programming experience more enjoyable. By identifying and fixing syntax errors and using Ruby's exception handling system, you can create robust, error-resistant programs.

Remember that errors are not your enemy; they are valuable feedback that helps you learn and grow as a programmer. Embrace errors, learn from them, and keep coding!