Eigenclass model: Difference between revisions

Revision as of 08:48, 13 December 2012

Revision as of 17:20, 14 December 2012

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In Smalltalk, every class has its own metaclass, and metaclass inheritance parallels class inheritance.

In 1988, [[Luca Cardelli]] introduced the notion of ''power types''<ref>

However, a full and consistent application of the eigenclass model appeared first (and only) in the

{{cite web | author=Luca Cardelli | url=http://www.daimi.au.dk/~madst/tool/tool2004/papers/structural.pdf | title=Structural Subtyping and the Notion of Power Type}}</ref>

[[Ruby (programming language)|Ruby programming language]].

which can be regarded as type-theoretic counterparts to eigenclasses.

The notion has later been adopted in the field of [[Metamodeling|metamodelling]].<ref>{{cite journal |last=Odell |first=James |title=Power Types |journal=Journal of Object-Oriented Programming |volume=7 |year=1994 |number=2 |page=8-12}}</ref>

<ref>

{{cite web | author=C. Gonzalez-Perez, B. Henderson-Sellers | url=http://www.ie.inf.uc3m.es/grupo/docencia/reglada/ASDM/GonzalezPerez06.pdf | title=A powertype-based metamodelling framework}}</ref>

(Nowadays, the single word ''"powertypes"'' is preferred.)

However, aA full and consistent application of the eigenclass model appeared firstin (and1995 only)as ina core part of the

[[Ruby (programming language)|Ruby programming language]].,

created by [[Yukihiro Matsumoto]].

The term ''"eigenclass"''

appearedemerged around 2005 in the Ruby community.

In 2008,

the term has been established in an authoritative book,<ref>{{cite book | publisher=O'Reilly Media | author=David Flanagan, Yukihiro Matsumoto | url=http://oreilly.com/catalog/9780596516178/ | title=The Ruby Programming Language | isbn=978-0-596-51617-8}}</ref> replacing the previously used ''"singleton class"''

(although in Ruby 1.9, the corresponding introspection method is still named <code>singleton_class</code>).

By simplification, the development history of the eigenclass model can be viewed as a 3-stage extension of a universality principle, summarized by the following table:

<table style="border-collapse:collapse;" border="1" cellpadding="3">

<tr>

<th>Year</th><th>Inventor</th>

<th>The principle</th>

<th>&hellip; in terms of the eigenclass model</th>

</tr>

<tr>

<td style="white-space:nowrap">c. 1980</td>

<td>Jim Althoff<ref>

{{cite web | url=http://mail.python.org/pipermail/python-dev/2001-May/014508.html | title=&#91;Python-Dev&#93; Classes and Metaclasses in Smalltalk }}</ref>

</td>

<td>Every class has its own metaclass.</td>

<td>Every class has an eigenclass.</td>

</tr>

<tr>

<td>c. 1988</td>

<td>Luca Cardelli</td>

<td>Every type has a power type.</td>

<td>Every class and every eigenclass has an eigenclass.</td>

</tr>

<tr>

<td>c. 1995</td>

<td>Yukihiro Matsumoto</td>

<td colspan=2 style="text-align:center">Every object has an eigenclass.</td>

</tr>

</table>

== {{anchor|canonical structure}} The canonical structure of &#1013; ==