Metaobjektu protokolu uzlabošana ģenerisko funkciju invokācijai
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Abstract
Common Lisp Object System (CLOS) ir pilna objektorientēta programmēšanas sistēma
priekš valodas Common Lisp, izstrādāta ap 1986. gadu kā daļa no ANSI Common Lisp
standarta. Tajā pašā laikā parādījās uz metaobjektu protokoliem (MOP) balstīta
pieeja augsta līmeņa valodu projektēšanā. Šī pieeja tika realizēta priekš CLOS
un ļauj paplašināt vai pielāgot sistēmu priekš lietotāja konkrētām vajadzībām.
Kopš tā parādīšanās, pašā CLOS MOP nekādas izmaiņas netika veiktas. Taču visu
šo gadu laikā tika sakrāta liela pieredze MOP izmantošanā un parādījās jaunas
idejas CLOS paplašināšanā, it īpaši attiecībā uz ģeneriskajām funkcijām. Tika
konstatēts, ka CLOS MOP ir dažreiz neērts un ir nepietiekami izteiksmīgs, kas
padara noteiktu CLOS paplašinājumu realizāciju pārāk sarežģītu vai vienkārši
neiespējamu, neieviešot izmaiņas pašā MOP.
Piemēram, ar šādām grūtībām saskarās nesenajos pētījumos par ģenerisko funkciju
paplašinājumiem. Lai palīdzētu risināt šīs problēmas, šajā darbā tiek vispirms
piedāvātas noteiktas izmaiņas CLOS MOP arhitektūrā, ieskaitot jaunu mehānismu
ieviešanu protokolā, kas dod smalkāku kontroli pār CLOS uzvedību. Balstoties uz
šīm izmaiņām, darbā tiek realizēti problēmātiskie ģenerisko funkciju invokācijas
mehānismi - filtrēta un predikātu novirzīšana - daudz vienkāršākajā veidā. Pie
tam, alternatīva protokola arhitektūra dod iespēju veidot lietotāja definētus
specializatorus, kā arī risina efektivitātes problēmas, kas ir sastopamas gan
standarta, gan jaunos novirzīšanas mehānismos.
The Common Lisp Object System (CLOS) is a complete object-oriented programming system for Common Lisp, designed as part of ANSI Common Lisp standard ca. 1986. The approach to high-level language design based on metaobject protocols (MOP) was developed at the same time and was implemented for CLOS to provide means for the user to modify and extend its behavior according to his or her needs. The CLOS MOP has never been revised since its appearance. The experience gained over the years and the new ideas on how to extend CLOS, especially in the area of generic functions, have revealed that the CLOS MOP is sometimes inconvenient to use and is insufficiently expressive, which makes certain extensions to CLOS unnecessarily complicated or simply impossible without modifying the MOP itself. In particular, such difficulties have been encountered in recent publications on extending generic functions. In order to address these difficulties, the thesis first proposes certain changes to the design of the CLOS MOP and introduces new features into the protocol that allow for a finer control over the CLOS behavior. The thesis then takes advantage of these changes to implement the problematic generic function invocation mechanisms, filtered and predicate dispatch, in a more straightforward way. The alternative design also provides the ability to create custom specializers and addresses efficiency issues, encountered in the standard and custom dispatch mechanisms.
The Common Lisp Object System (CLOS) is a complete object-oriented programming system for Common Lisp, designed as part of ANSI Common Lisp standard ca. 1986. The approach to high-level language design based on metaobject protocols (MOP) was developed at the same time and was implemented for CLOS to provide means for the user to modify and extend its behavior according to his or her needs. The CLOS MOP has never been revised since its appearance. The experience gained over the years and the new ideas on how to extend CLOS, especially in the area of generic functions, have revealed that the CLOS MOP is sometimes inconvenient to use and is insufficiently expressive, which makes certain extensions to CLOS unnecessarily complicated or simply impossible without modifying the MOP itself. In particular, such difficulties have been encountered in recent publications on extending generic functions. In order to address these difficulties, the thesis first proposes certain changes to the design of the CLOS MOP and introduces new features into the protocol that allow for a finer control over the CLOS behavior. The thesis then takes advantage of these changes to implement the problematic generic function invocation mechanisms, filtered and predicate dispatch, in a more straightforward way. The alternative design also provides the ability to create custom specializers and addresses efficiency issues, encountered in the standard and custom dispatch mechanisms.