Errors and Exceptions

Summary

With a lot of programming languages, the exception hierarchy is built around two categories:

Errors - indicates serious problems that a reasonable application should not try to catch
Exceptions - indicates conditions that a reasonable application might want to catch

One general way to think about it is if the exception happens during the runtime (exectuion) of the application. A SyntaxError

Each of these have subclasses that depend on the language. For example, in Java it might look like:

Errors Descendants

Error Descendants

AssertionError - thrown when an assertion has failed
LinkageError - thrown when a class dependency has some form of incompatibility

Exception Descendants

InterruptedException - thrown when a thread is active, but is somehow interrupted in the process
RuntimeException - Thrown during normal execution of the application and operation of the Java Virtual Machine. This category can include common exceptions like ArithmeticException and IndexOutOfBoundsException

Ruby

In Ruby, exceptions are just classes in Ruby. The exception hierarchy is made up of all the classes that inherit from the Exception class. Some examples include:

NoMemoryError
ScriptError
- LoadError
- NotImplementedError
- SyntaxError
SecurityError
SignalException
- Interrupt
StandardError – default for rescue
- ArgumentError
  - UncaughtThrowError
- EncodingError
- FiberError
- IOError
  - EOFError
- IndexError
  - KeyError
  - StopIeration
- LocalJumpError
- NameError
  - NoMethodError
- RangeError
  - FloatDomainError
- RegexpError
- RuntimeError – default for raise
- SystemCallError
  - Errno::
- ThreadError
- TypeError
- ZeroDivisionError
SystemExit
SystemStackError

https://ruby-doc.org/core-2.5.0/Exception.html

RuntimeError

RuntimeError is important because it is the default error class that is used when calling the standard Kernel#raise method that we all use to handle exceptions (e.g. in your code, you might raise.

Rescues

Exceptions are arranged into a class tree so you can easily rescue similar types of exceptions.

begin
  do_something
rescue StandardError => e
end