Exception

        # Exception < Object

(from ruby core)
---
Class Exception and its subclasses are used to communicate between
Kernel#raise and `rescue` statements in `begin ... end` blocks.

An Exception object carries information about an exception:
*   Its type (the exception's class).
*   An optional descriptive message.
*   Optional backtrace information.


Some built-in subclasses of Exception have additional methods: e.g.,
NameError#name.

## Defaults

Two Ruby statements have default exception classes:
*   `raise`: defaults to RuntimeError.
*   `rescue`: defaults to StandardError.


## Global Variables

When an exception has been raised but not yet handled (in `rescue`,
`ensure`, `at_exit` and `END` blocks), two global variables are set:
*   `$!` contains the current exception.
*   `$@` contains its backtrace.


## Custom Exceptions

To provide additional or alternate information, a program may create
custom exception classes that derive from the built-in exception
classes.

A good practice is for a library to create a single "generic" exception
class (typically a subclass of StandardError or RuntimeError) and have
its other exception classes derive from that class. This allows the user
to rescue the generic exception, thus catching all exceptions the
library may raise even if future versions of the library add new
exception subclasses.

For example:

    class MyLibrary
      class Error < ::StandardError
      end

      class WidgetError < Error
      end

      class FrobError < Error
      end

    end

To handle both MyLibrary::WidgetError and MyLibrary::FrobError the
library user can rescue MyLibrary::Error.

## Built-In Exception Classes

The built-in subclasses of Exception are:

*   NoMemoryError
*   ScriptError
    *   LoadError
    *   NotImplementedError
    *   SyntaxError

*   SecurityError
*   SignalException
    *   Interrupt

*   StandardError
    *   ArgumentError
        *   UncaughtThrowError

    *   EncodingError
    *   FiberError
    *   IOError
        *   EOFError

    *   IndexError
        *   KeyError
        *   StopIteration
            *   ClosedQueueError


    *   LocalJumpError
    *   NameError
        *   NoMethodError

    *   RangeError
        *   FloatDomainError

    *   RegexpError
    *   RuntimeError
        *   FrozenError

    *   SystemCallError
        *   Errno::*

    *   ThreadError
    *   TypeError
    *   ZeroDivisionError

*   SystemExit
*   SystemStackError
*   fatal


---
# Class methods:

    exception
    json_create
    new
    to_tty?

# Instance methods:

    ==
    as_json
    backtrace
    backtrace_locations
    cause
    exception
    full_message
    inspect
    message
    set_backtrace
    to_json
    to_s