Ruby Rescue Exception Type

While it may be tempting to rescue every child of the exception class it is generally considered bad practice due to the way the ruby exception hierarchy is structured.

Ruby rescue exception type.

Become a better developer. You ve learned about errors in ruby basic exception handling the rescue begin keywords. How to handle an exception. That s because ruby uses exceptions for things other than errors.

In this article you ll learn how to use the rescue keyword in combination with begin to handle ruby exceptions the most effective way. Ruby s exception hierarchy is used to differentiate between different types of errors while giving you the ability to rescue from a group of errors without specifying all of them. This method can be used to retrieve a specific exception message from a raised exception object. Ryan davis s ruby quickref says without explanation.

For each rescue clause in the begin block ruby compares the raised exception against each of the parameters in turn. Although libraries can define their own exception subclasses the list of built in exception subclasses on ruby 2 5 looks like this. Ruby s exception handling mechanism is simple. The code above will rescue every exception.

The reason for this is that while all ruby exceptions and errors are an extension of the exception class many of them are reserved for use internally by ruby. It also uses them to handle messages from the operating system called signals if you ve ever pressed ctrl c to exit a program you ve used a signal. At its core every ruby exception stems from a built in exception class and includes a handful of built in methods but the most commonly used exception method is message. It ll break your program in weird ways.

It will be unkillable except by kill 9. The general syntax for the rescue statement is as follows. The code in an else clause is executed if the code in the body of the begin statement runs to completion without. Ruby does require some form of begin to appear before the rescue.

Exception is the root of ruby s exception hierarchy so when you rescue exception you rescue from everything including subclasses such as syntaxerror loaderror and interrupt. Rescuing signalexception prevents the program from responding correctly to signals. Or i will stab you. The match will succeed if the exception named in the rescue clause is the same as the type of the currently thrown exception or is a superclass of that exception.

Rescuing interrupt prevents the user from using ctrlc to exit the program. What s the right thing to do.