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2 Introduction

Due to restrictions in the Emacs Lisp language, CLOS cannot be completely supported, and a few functions have been added in place of setf.

EIEIO supports the following features:

  1. A structured framework for the creation of basic classes with attributes and methods using singular inheritance similar to CLOS.
  2. Type checking, and slot unbinding.
  3. Method definitions similar to CLOS.
  4. Simple and complex class browsers.
  5. Edebug support for methods.
  6. Imenu updates.
  7. Byte compilation support of methods.
  8. Help system extensions for classes and methods.
  9. Several base classes for interesting tasks.
  10. Simple test suite.
  11. Public and private classifications for slots (extensions to CLOS)
  12. Customization support in a class (extension to CLOS)

Here are some important CLOS features that EIEIO presently lacks:

Method dispatch
EIEO does not support method dispatch for built-in types and multiple arguments types. In other words, method dispatch only looks at the first argument, and this one must be an EIEIO type.
Support for metaclasses
There is just one default metaclass, eieio-default-superclass, and you cannot define your own. The :metaclass tag in defclass is ignored. Also, functions like `class-of' and `find-class', which should return instances of the metaclass, behave differently in EIEIO in that they return symbols or plain structures instead.
EQL specialization
EIEIO does not support it.
:around method tag
This CLOS method tag is non-functional.
:default-initargs in defclass
Each slot has an :initarg tag, so this is not really necessary.
Mock object initializers
Each class contains a mock object used for fast initialization of instantiated objects. Using functions with side effects on object slot values can potentially cause modifications in the mock object. EIEIO should use a deep copy but currently does not.