Ruby on Rails® for Microsoft Developers

4.4. Exception Handling

In the previous examples, it was casually mentioned how Ruby raises this or that type of error, if you perform an illicit operation. Just like C#, VB, and any other respectable modern programming language out there, Ruby offers full support for handling exceptions.

This is how you would typically "catch an exception" in C# and VB:

C#

int a = 5;
int b = 0;
int div;

try
{
    div = a / b;
    Console.WriteLine("This is never written");
}
catch (Exception ex)
{
    Console.WriteLine("Oops... {0}", ex.Message);
}

VB

Dim a As Integer = 5
Dim b As Integer = 0
Dim div As Integer

Try
    div = a / b
    Console.WriteLine("This is never written")
Catch ex As Exception
    Console.WriteLine("Oops... {0}", ex.Message)
End Try

In both cases a division by zero is attempted within the try statement, and the exception raised is caught by the catch clause, which prints "Oops... Attempted to divide by zero." in C#'s case and "Oops... Arithmetic operation resulted in an overflow." for VB. Ruby works in the same way through begin/rescue as shown here:

a = 5
b = 0

begin
  div = a /b
  puts "This is never written"
rescue Exception => ex
  puts "Oops... #{ex.message}"
end

The rescue clause sets the variable ex to reference an instance of the given error class. The Exception class is the root of all error classes in Ruby, and as such it catches any errors that can possibly be raised.

It is generally a bad idea to rescue all the exceptions in a single catch clause.

If you didn't specify Exception