eieio: Introduction
2 Introduction
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First off, please note that this manual cannot serve as a complete
introduction to object oriented programming and generic functions in
LISP. Although EIEIO is not a complete implementation of the Common
Lisp Object System (CLOS) and also differs from it in several aspects,
it follows the same basic concepts. Therefore, it is highly recommended
to learn those from a textbook or tutorial first, especially if you only
know OOP from languages like C++ or Java. If on the other hand you are
already familiar with CLOS, you should be aware that EIEIO does not
implement the full CLOS specification and also differs in some other
aspects which are mentioned below (also 
CLOS compatibility).
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)
Due to restrictions in the Emacs Lisp language, CLOS cannot be
completely supported, and a few functions have been added in place of
setf. 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 ‘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 can have an ‘:initform’ 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.
Info Catalog
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