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diff --git a/SIP/virtual-traits/sip-0000X.xhtml b/SIP/virtual-traits/sip-0000X.xhtml new file mode 100644 index 0000000000..170a1ec436 --- /dev/null +++ b/SIP/virtual-traits/sip-0000X.xhtml @@ -0,0 +1,341 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml"> +<head> + <title>Virtual Traits for Scala</title> + <meta name="sip" content="0000X"/> + <meta name="author" content="Anders Bach Nielsen"/> + <meta name="version" content="0"/> + <meta name="type" content="standards"/> + <meta name="status" content="submission"/> + <meta name="created" content="2008-08-21"/> + <meta name="updated" content="2008-11-24"/> + <meta name="scala-version" content="2.8.0.final-"/> + <meta name="owner-contact" content="mailto:andersbach.nielsen@epfl.ch"/> + <!-- <meta name="discussion" content="[URI]"/> --> + <!-- <link rel="auxiliary" href="[URI]" type="[mime type]"/> --> + <!-- <link rel="replaces" href="[URI]" type="application/xhtml+xml"/> --> + <link rel="depends-on" href="PATH-TO-TRAIT-PARAMETERS-SIP" type="application/xhtml+xml"/> + <!-- Stylesheet --> + <link rel="stylesheet" href="http://lampsvn.epfl.ch/svn-repos/scala/sip/trunk/sip.css" type="text/css"/> +</head> +<body> + <a name="top"></a> + <h1>Virtual Traits for Scala</h1> + + <h2>Abstract</h2> + + <p>This document describes the design, integration and implementation + of Virtual Traits (VT) into the Scala language. Virtual traits in + Scala are modeled after the BETA [<a + href="#madsen93:_objec_orien_progr_beta_progr_languag">1</a>] and + gbeta [<a href="#ernst99b">3</a>] notion of virtual classes [<a + href="#Mads89a">2</a>, <a href="#1111062">4</a>]. </p> + + <h2>Contents</h2> + + <ul> + <li><a href="#motivation">Motivation</a> + <ul> + <li><a href="#goals">Goals</a></li> + <li><a href="#usecases">Use cases</a></li> + <li><a href="#usecasedetail">Use cases in detail</a></li> + <li><a href="#futuregoals">Future goals that extend beyond this proposal</a></li> + </ul> + </li> + <li><a href="#languagespec">Language specification changes</a></li> + <li><a href="#implementation">Implementation</a></li> + <li><a href="#references">References</a></li> + </ul> + + + <a name="motivation"></a> + <h2>Motivation</h2> + + <p>The Scala language already has abstract type members that behave + like the types of virtual classes, however this is only for + types. Scala supports both classes and traits, where traits act as + mixins that can be composed together to create classes. The reason + why there are both classes and traits, is to support the + interoperability with Java which has only classes and for this + reason classes are treated specially in the compiler.</p> + + <p>Using abstract type members and a complicated rewriting scheme it + is possible to create virtual classes manually, but there are + several typing issues which will be covered later. We will in this + proposal show the extensions to the Scala language specification to + include virtual traits, the rewriting scheme for translating virtual + trait programs into regular Scala programs and discuss the + implementation of this in the Scala compiler.</p> + + <p>This proposal builds upon the parametrized traits.</p> + + <a name="goals"></a> + <h3>Goals</h3> + + <ul> + <li>Present the additions and changes to the Scala Language + Specification to cover Virtual Traits.</li> + <li>Show in detail the rewriting scheme used in the translation of + Scala programs with virtual traits to programs in Scala + proper.</li> + <li>Present a sample implementation in the Scala compiler.</li> + </ul> + + + <a name="usecases"></a> + <h3>Use cases</h3> + + <ol> + <li><a href="#usecase1">Initial binding of virtual trait</a></li> + <li><a href="#usecase2">Further binding of a virtual trait</a></li> + <li><a href="#usecase3">Final binding of a virtual trait</a></li> + <li><a href="#usecase4">Diamond inheritance involving virtual traits</a></li> + <li><a href="#usecase5">Virtual traits with nested virtual traits</a></li> + </ol> + + <a name="usecasedetail"></a> + <h3>Use cases in detail</h3> + + <a name="usecase1"></a> + <h4>(1) Initial binding of virtual trait</h4> + + <p></p> + + <pre> + <b>trait</b> A <: { ... } + <b>trait</b> B <: A { ... } + <b>trait</b> C <: Foo <b>with</b> B { ... } + </pre> + + <a name="usecase2"></a> + <h4>(2) Further binding of a virtual trait</h4> + + <p></p> + + <pre> + <b>override trait</b> A <: { ... } + <b>override trait</b> B <: { ... } + <b>override trait</b> C <: Bar { ... } + </pre> + + <a name="usecase3"></a> + <h4>(3) Final binding of a virtual trait</h4> + + <p></p> + + <pre> + <b>override trait</b> A + <b>override trait</b> B { ... } + <b>override trait</b> C <b>extends</b> Baz { ... } + </pre> + + <a name="usecase4"></a> + <h4>(4) Diamond inheritance involving virtual traits</h4> + + <p></p> + + <pre> + <b>trait</b> A { + <b>trait</b> V <: { ... } + } + <b>trait</b> B <b>extends</b> A { + <b>override trait</b> V <: { ... } + } + <b>trait</b> C <b>extends</b> A { + <b>override trait</b> V <: { ... } + } + <b>trait</b> D <b>extends</b> B <b>with</b> C { + <b>override trait</b> V <: { ... } + } + </pre> + + <a name="usecase5"></a> + <h4>(5) Virtual traits with nested virtual traits</h4> + + <p></p> + + <pre> + <b>trait</b> A { + <b>trait</b> V <: { + <b>trait</b> W <: { ... } + } + } + <b>trait</b> B <b>extends</b> A { + <b>override trait</b> V <: { + <b>override trait</b> W <: { ... } + } + } + </pre> + + <a name="futuregoals"></a> + <h3>Future goals that extend beyond this proposal</h3> + + <ul> + <li>Having virtual classes, these would have to be converted from + classes to traits and so</li> + </ul> + + <a name="languagespec"></a> + <h2>Language specification changes</h2> + + This section will cover the changes to the Scala language, both the + syntactic and sematic changes that are nessesary to make virtual + traits work under Scala. + + <p> + Normal declaration of a trait in Scala. + </p> + <pre> + trait Foo { ... } + </pre> + + <pre> + TmplDef ::= ['case'] 'class' ClassDef + | ['case'] 'object' ObjectDef + | ['override'] 'trait' TraitDef + +TraitDef ::= id [TypeParamClause] TraitTemplateOpt + +TraitTemplateOpt ::= TraitExtends TraitTemplate + | [['extends'] TemplateBody ] + | '<:' TemplateBody + +TraitExtends ::= 'extends' | '<:' + + +---------- FLAGS ------------- + +TRAIT + DEFERED + ! OVERRIDE => Initial binding +TRAIT + DEFERED + OVERRIDE => Further binding +TRAIT + ! DEFERED + OVERRIDE => Final binding + +classes that extend virtuals are marked with a VIRTUALSUBCLASS + + </pre> + + <h3>Syntactic</h3> + + From the virtual class litterateur there is a distinction between + the initial binding and the further binding of a virtual class. To + have the same expressiveness in Scala this is the way to declare a + initial binding of a virtual trait. + <pre> + trait Bar <: { ... } + </pre> + To be able to tell the difference between a initial and a further + binding of a trait on the syntactical level, further bindings are + written as. + <pre> + override trait Bar <: { ... } + </pre> + + <h3>Semantic</h3> + + + <a name="implementation"></a> + <h2>Implementation</h2> + + + + <a name="references"></a> + <h2>References</h2> + + <table> + <tr valign="top"> + <td align="right"> + [<a name="madsen93:_objec_orien_progr_beta_progr_languag">1</a>] + </td> + <td> + Ole Lehrmann Madsen, Kristen Nygaard, and Birger Møller-Pedersen. + <em>Object-Oriented Programming in The Beta Programming Language</em>. + Addison-Wesley, 1993. + [ <a href="sip-0000X-1.xhtml#madsen93:_objec_orien_progr_beta_progr_languag">bib</a> ] + </td> + </tr> + + <tr valign="top"> + <td align="right"> + [<a name="Mads89a">2</a>] + </td> + <td> + Ole Lehrmann Madsen and Birger Møller-Pedersen. + Virtual classes: A powerful mechanism in object-oriented + programming. + In <em>Proceedings OOPSLA'89, ACM SIGPLAN Notices</em>, volume 24, + 10, pages 397-406, October 1989. + [ <a href="sip-0000X-1.xhtml#Mads89a">bib</a> ] + </td> + </tr> + + <tr valign="top"> + <td align="right"> + [<a name="ernst99b">3</a>] + </td> + <td> + Erik Ernst. + <em>gbeta - a Language with Virtual Attributes, Block Structure, + and Propagating, Dynamic Inheritance</em>. + PhD thesis, Department of Computer Science, University of Aarhus, + Århus, Denmark, 1999. + [ <a href="sip-0000X-1.xhtml#ernst99b">bib</a> ] + </td> + </tr> + + <tr valign="top"> + <td align="right"> + [<a name="1111062">4</a>] + </td> + <td> + Erik Ernst, Klaus Ostermann, and William R. Cook. + A virtual class calculus. + In <em>POPL '06: Conference record of the 33rd ACM SIGPLAN-SIGACT + symposium on Principles of programming languages</em>, pages 270-282, New York, + NY, USA, 2006. ACM Press. + [ <a href="sip-0000X-1.xhtml#1111062">bib</a> ] + </td> + </tr> + + <tr valign="top"> + <td align="right"> + [<a name="Erns01a">5</a>] + </td> + <td> + Erik Ernst. + Family polymorphism. + In J. L. Knudsen, editor, <em>ECOOP 2001</em>, number 2072 in LNCS, + pages 303-326. Springer Verlag, 2001. + [ <a href="sip-0000X-1.xhtml#Erns01a">bib</a> ] + </td> + </tr> + + <tr valign="top"> + <td align="right"> + [<a name="EE99">6</a>] + </td> + <td> + Erik Ernst. + Propagating class and method combination. + In Rachid Guerraoui, editor, <em>Proceedings ECOOP'99</em>, LNCS 1628, + pages 67-91, Lisboa, Portugal, June 1999. Springer-Verlag. + [ <a href="sip-0000X-1.xhtml#EE99">bib</a> ] + </td> + </tr> + + <tr valign="top"> + <td align="right"> + [<a name="aracic06:_overv_of_caesarj">7</a>] + </td> + <td> + Ivica Aracic, Vaidas Gasiunas, Mira Mezini, and Klaus Ostermann. + An overview of caesarj. + In <em>Transactions on Aspect-Oriented Software Development I</em>, + volume 3880/2006 of <em>Lecture Notes in Computer Science</em>, pages 135-173. + Springer Berlin / Heidelberg, 2006. + [ <a href="sip-0000X-1.xhtml#aracic06:_overv_of_caesarj">bib</a> ] + </td> + </tr> + </table> + +</body> +</html> |