DOCSLIB.ORG

Mixin-Based Inheritance

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Mixin-Based Inheritance Mixin-based Inheritance Gilad Bracha∗ William Cook Department of Computer Science Hewlett-Packard Laboratories University of Utah 1501 Page Mill Road Salt Lake City, UT 84112 Palo Alto, CA 94303-0969 Abstract prefix methods cannot be replaced; instead, the prefix may use the command inner to invoke the extended The diverse inheritance mechanisms provided by method code supplied by the subpattern. Given that the Smalltalk, Beta, and CLOS are interpreted as differ- code in a prefix is executed in any of its extensions, Beta ent uses of a single underlying construct. Smalltalk and enforces a degree of behavioral consistency between a Beta differ primarily in the direction of class hierarchy pattern and its subpatterns. growth. These inheritance mechanisms are subsumed in The underlying mechanism of inheritance is the same a new inheritance model based on composition of mix- for Beta and Smalltalk [3]. The difference between them ins, or abstract subclasses. This form of inheritance lies in whether the extensions to an existing definition can also encode a CLOS multiple-inheritance hierarchy, have precedence over and may refer to previous defini- although changes to the encoded hierarchy that would tions (Smalltalk), or the inherited definition has prece- violate encapsulation are difficult. Practical application dence over and may refer to the extensions (Beta). This of mixin-based inheritance is illustrated in a sketch of model shows that Beta and Smalltalk have inverted in- an extension to Modula-3. heritance hierarchies: a Smalltalk subclass refers to its parent using super just as a Beta prefix refers to its subpatterns using inner. 1 Introduction In the Common Lisp Object System (CLOS) and its predecessor, Flavors [13], multiple parent classes may A variety of inheritance mechanisms have been devel- be merged during inheritance. A class's ancestor graph oped for object-oriented programming languages. These is linearized so that each ancestor occurs only once [7]. systems range from classical Smalltalk single inheri- With standard method combination for primary meth- tance [8], through the safer prefixing of Beta [12, 10], ods, the function call-next-method is used to invoke the to the complex and powerful multiple inheritance com- next method in the inheritance chain. binations of CLOS [6, 9]. These languages have similar CLOS supports mixins as a useful technique for build- object models, and also share the view that inheritance ing systems out of mixable attributes. A mixin is an is a mechanism for incremental programming. However, abstract subclass; i.e. a subclass definition that may they differ widely in the kind of incremental changes be applied to different superclasses to create a related supported. family of modified classes. For example, a mixin might In Smalltalk, subclasses can add additional methods be defined that adds a border to a window class; this or replace existing methods in the parent class. As a mixin could be applied to any kind of window to cre- result, there is no necessary relationship between the ate a bordered-window class. Semantically, mixins are behavior of instances of a class and the instances of its closely related to Beta prefixes. subclasses. The subclass methods can invoke any of the Linearization has been criticized for violating encap- original superclass methods via super. sulation, because it may change the parent-child re- In Beta, a subpattern (subclass) definition is viewed as lationships among classes in the inheritance hierarchy an extension of a previously defined prefix pattern. As [16, 17]. But the mixin technique in CLOS depends in Smalltalk, new methods may be defined. However, directly upon linearization and modification of parent- ∗Supported by grant CCR-8704778 from the National Science child relationships. Rather than avoid mixins because Foundation. they violate encapsulation, we argue that linearization Appeared in Proceedings of the ACM Conference on is an implementation technique for mixins that obscures Object-Oriented Programming: Systems, Languages, and their true nature as abstractions. Applications (OOPSLA) October 21- 25, 1990. By modest generalization of the inheritance models c 1990 ACM. Copied by permission. in Smalltalk and Beta, a form of inheritance based on 1 composition of mixins is derived. Mixin-based inheri- the Person display method using super display to display tance supports both the flexibility of Smalltalk and the the name, and then displays the degree. The net effect security of Beta. It also supports the direct encoding would be to print \A. Smith Ph.D.". It would also be of CLOS multiple inheritance hierarchies without du- possible to prefix the name, as in the case of titles like plication of subclass definitions. However, since the hi- \Dr.", by printing the title before calling super. erarchy is encoded as an explicit collection of linearized The subclass Graduate specifies only how Graduates inheritance chains rather than as a single inheritance differ from Persons [19]. This difference may be indi- graph, some changes to the hierarchy (especially if they cated explicitly as a delta, or set of changes. In this case might violate Snyder's notion of encapsulation) cannot the set of changes is simply the new display method. easily be made. The original definition is also just a display method. Section 2 discusses the single-inheritance languages When combined, the new display method replaces the Smalltalk and Beta and shows that they support very original. different uses of a single underlying construct. Sec- To formalize this process, objects are represented as tion 3 analyzes multiple inheritance and linearization records whose fields contain methods [1, 15, 18, 3]. The in CLOS, with special focus on support for mixins. expression fa1 7! v1; ··· ; an 7! vng represents a record Section 4 presents a generalized inheritance mechanism with fields a1; : : : ; an and associated values v1; : : : ; vn. that supports the style of inheritance in Beta, Smalltalk, The expression r:a represents selection of field a from and CLOS, with explicit support for mixins. In Sec- a record r. Record combination is a binary operator, tion 5 we sketch an extension to Modula-3 that illus- ⊕, that forms a new record with the fields from its two trates the use of generalized inheritance. Finally, Sec- arguments, where the value is from the left argument tion 6 summarizes our conclusions. in case the same field is present in both records. For example, fa 7! 3; b 7! `x'g ⊕ fa 7! true; c 7! 8g replaces the right value of a to produce fa 7! 3; b 7! `x'; c 7! 8g. 2 Single Inheritance Languages To interpret super, it is necessary for the delta, or modifications, to access the original method inherited 2.1 Smalltalk Inheritance from Person. This is achieved by supplying the parent Inheritance in Smalltalk is a mechanism for incremental class methods as a parameter to the delta. The resulting derivation of classes. Smalltalk inheritance was adapted inheritance mechanism is an asymmetric combination of from Simula [5, 14], and serves as the prototypical in- a parametric delta ∆ and a parent specification P : heritance mechanism. The primary subtlety in the pro- C = ∆(P ) ⊕ P: cess of inheritance is the interpretation of the special variables self and super. Self represents recursion, or This definition is a form of single inheritance: P refers self-reference, within the object instance being defined. to the inherited parent while ∆ is an explicit set of The interpretation of self has been addressed in previ- changes. The two occurrences of P do not indicate that ous work [3, 4, 15]; in this paper we focus on the in- it is instantiated twice, but that its information is used terpretation of super. Consider the following pair of in two contexts: for the interpretation of super and to Smalltalk classes. provide methods for the subclass. Suppressing the in- class Person terpretation of hidden instance variables, the example instance variables: name above has the following form. method: display P = fdisplay 7! name.displayg name display ∆(s) = fdisplay 7! s.display, degree.displayg ∆(P ) = fdisplay 7! name.display, degree.displayg class Graduate superclass: Person Although deltas were introduced to make specifica- instance variables: degree tion of the inheritance mechanism more clear, deltas method: display are not independent elements of a Smalltalk program; super display. degree display they cannot stand on their own and are always part of a subclass definition, which has an explicit parent class. The class Person defines a name field and a method for In Smalltalk a subclass of Person may completely re- displaying the name. The subclass Graduate extends the place the display method with, for example, a routine display method to include the person's academic degree. that displays the time of day. In Smalltalk inheritance, For example, a graduate with name \A. Smith" and the subclass is in control: there is no way to define degree \Ph.D." would respond to the display method Person so that it forces subclasses to invoke its display by invoking the Graduate display method, which invokes method as part of their display operation. 2 2.2 Beta Inheritance resents any inner definitions supplied by subpatterns. For an instance of Person, the inner part of P 0 is bound Inheritance in Beta is designed to provide security from to the record of null methods: P 0(;). replacement of a method by a completely different A subpattern specifies additional attributes which method. Inheritance is supported in Beta by prefixing of may also refer to any further inner behavior in later definitions. Beta employs a single definitional construct, subpatterns. If the attributes defined in the subpattern the pattern, to express types, classes and methods. As are specified by ∆0, then the result of prefixing by P 0 is this generality can be confusing, we use a simpler syn- the following composition: tax that distinguishes among the different roles1.
Load more

Recommended publications
  • MANNING Greenwich (74° W
    Object Oriented Perl Object Oriented Perl DAMIAN CONWAY MANNING Greenwich (74° w. long.) For electronic browsing and ordering of this and other Manning books, visit http://www.manning.com. The publisher offers discounts on this book when ordered in quantity. For more information, please contact: Special Sales Department Manning Publications Co. 32 Lafayette Place Fax: (203) 661-9018 Greenwich, CT 06830 email: [email protected] ©2000 by Manning Publications Co. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by means electronic, mechanical, photocopying, or otherwise, without prior written permission of the publisher. Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in the book, and Manning Publications was aware of a trademark claim, the designations have been printed in initial caps or all caps. Recognizing the importance of preserving what has been written, it is Manning’s policy to have the books we publish printed on acid-free paper, and we exert our best efforts to that end. Library of Congress Cataloging-in-Publication Data Conway, Damian, 1964- Object oriented Perl / Damian Conway. p. cm. includes bibliographical references. ISBN 1-884777-79-1 (alk. paper) 1. Object-oriented programming (Computer science) 2. Perl (Computer program language) I. Title. QA76.64.C639 1999 005.13'3--dc21 99-27793 CIP Manning Publications Co. Copyeditor: Adrianne Harun 32 Lafayette
    [Show full text]
  • A Comparative Study on the Effect of Multiple Inheritance Mechanism in Java, C++, and Python on Complexity and Reusability of Code
    (IJACSA) International Journal of Advanced Computer Science and Applications, Vol. 8, No. 6, 2017 A Comparative Study on the Effect of Multiple Inheritance Mechanism in Java, C++, and Python on Complexity and Reusability of Code Fawzi Albalooshi Amjad Mahmood Department of Computer Science Department of Computer Science University of Bahrain University of Bahrain Kingdom of Bahrain Kingdom of Bahrain Abstract—Two of the fundamental uses of generalization in Booch, there are two problems associated with multiple object-oriented software development are the reusability of code inheritance and they are how to deal with name collisions from and better structuring of the description of objects. Multiple super classes, and how to handle repeated inheritance. He inheritance is one of the important features of object-oriented presents solutions to these two problems. Other researchers [4] methodologies which enables developers to combine concepts and suggest that there is a real need for multiple inheritance for increase the reusability of the resulting software. However, efficient object implementation. They justify their claim multiple inheritance is implemented differently in commonly referring to the lack of multiple subtyping in the ADA 95 used programming languages. In this paper, we use Chidamber revision which was considered as a deficiency that was and Kemerer (CK) metrics to study the complexity and rectified in the newer version [5]. It is clear that multiple reusability of multiple inheritance as implemented in Python, inheritance is a fundamental concept in object-orientation. The Java, and C++. The analysis of results suggests that out of the three languages investigated Python and C++ offer better ability to incorporate multiple inheritance in system design and reusability of software when using multiple inheritance, whereas implementation will better structure the description of objects Java has major deficiencies when implementing multiple modeling, their natural status and enabling further code reuse inheritance resulting in poor structure of objects.
    [Show full text]
  • Mixins and Traits
    ◦ ◦◦◦ TECHNISCHE UNIVERSITAT¨ MUNCHEN¨ ◦◦◦◦ ◦ ◦ ◦◦◦ ◦◦◦◦ ¨ ¨ ◦ ◦◦ FAKULTAT FUR INFORMATIK Programming Languages Mixins and Traits Dr. Michael Petter Winter 2016/17 What advanced techiques are there besides multiple implementation inheritance? Outline Design Problems Cons of Implementation Inheritance 1 Inheritance vs Aggregation 1 2 (De-)Composition Problems Lack of finegrained Control 2 Inappropriate Hierarchies Inheritance in Detail A Focus on Traits 1 A Model for single inheritance 1 2 Inheritance Calculus with Separation of Composition and Inheritance Expressions Modeling 2 3 Modeling Mixins Trait Calculus Mixins in Languages Traits in Languages 1 (Virtual) Extension Methods 1 Simulating Mixins 2 Squeak 2 Native Mixins Reusability ≡ Inheritance? Codesharing in Object Oriented Systems is often inheritance-centric. Inheritance itself comes in different flavours: I single inheritance I multiple inheritance All flavours of inheritance tackle problems of decomposition and composition The Adventure Game Door ShortDoor LockedDoor canPass(Person p) canOpen(Person p) ? ShortLockedDoor canOpen(Person p) canPass(Person p) The Adventure Game Door <interface>Doorlike canPass(Person p) canOpen(Person p) Short canPass(Person p) Locked canOpen(Person p) ShortLockedDoor ! Aggregation & S.-Inheritance Door must explicitely provide canOpen(Person p) chaining canPass(Person p) Doorlike must anticipate wrappers ) Multiple Inheritance X The Wrapper FileStream SocketStream read() read() write() write() ? SynchRW acquireLock() releaseLock() ! Inappropriate Hierarchies
    [Show full text]
  • Declaring Vars in Class Php
    Declaring Vars In Class Php Is Tobe Esculapian or misformed after aluminous Neall plopping so magnanimously? Forrest corresponds prolixly? Forbidden Osmund sometimes pargets any lilliputian yell guardedly. How variable as int, php in using interpolation rather than configured one of people prefer to override whatever information useful whenever you call it leads to expose parts that We daily work with advertisers relevant to our readers. Acceptable in php programmers and retry saving again, declaration must be. Declaring a property but a class is an exact task use one table the keyword public protected or private followed by a normal variable declaration If. If you wrong there holding an IE bug with var a foo only declaring a global for file scope. Your class declaration format is declared protected field? You help also define methods in the class that allow tool to manipulate the values of object properties and perform operations on objects. PHP Class Properties Tutorials by Supun Kavinda. An amazon associate we declare the class in declarations as containers for our clients in the usages of a name given client exits and in? How clean and in declaring a class declaration scope in the vars of that are their parent selector. Using long array syntax array 1 2 3 for declaring arrays is generally. By declaring a class declaration, classes and see for? It turns out some interview situations, every time to magento source and other class names but you have a common occurrence, therefore considered a value. The var keyword in PHP is used to declare the property or variable of class which is primitive by default The var keyword is alike as out when declaring variables or root of a class Note The var keyword was deprecated from version 50.
    [Show full text]
  • Learning Javascript Design Patterns
    Learning JavaScript Design Patterns Addy Osmani Beijing • Cambridge • Farnham • Köln • Sebastopol • Tokyo Learning JavaScript Design Patterns by Addy Osmani Copyright © 2012 Addy Osmani. All rights reserved. Revision History for the : 2012-05-01 Early release revision 1 See http://oreilly.com/catalog/errata.csp?isbn=9781449331818 for release details. ISBN: 978-1-449-33181-8 1335906805 Table of Contents Preface ..................................................................... ix 1. Introduction ........................................................... 1 2. What is a Pattern? ...................................................... 3 We already use patterns everyday 4 3. 'Pattern'-ity Testing, Proto-Patterns & The Rule Of Three ...................... 7 4. The Structure Of A Design Pattern ......................................... 9 5. Writing Design Patterns ................................................. 11 6. Anti-Patterns ......................................................... 13 7. Categories Of Design Pattern ............................................ 15 Creational Design Patterns 15 Structural Design Patterns 16 Behavioral Design Patterns 16 8. Design Pattern Categorization ........................................... 17 A brief note on classes 17 9. JavaScript Design Patterns .............................................. 21 The Creational Pattern 22 The Constructor Pattern 23 Basic Constructors 23 Constructors With Prototypes 24 The Singleton Pattern 24 The Module Pattern 27 iii Modules 27 Object Literals 27 The Module Pattern
    [Show full text]
  • Mixin-Based Programming in C++1
    Mixin-Based Programming in C++1 Yannis Smaragdakis Don Batory College of Computing Department of Computer Sciences Georgia Institute of Technology The University of Texas at Austin Atlanta, GA 30332 Austin, Texas 78712 [email protected] [email protected] Abstract. Combinations of C++ features, like inheritance, templates, and class nesting, allow for the expression of powerful component patterns. In particular, research has demonstrated that, using C++ mixin classes, one can express lay- ered component-based designs concisely with efficient implementations. In this paper, we discuss pragmatic issues related to component-based programming using C++ mixins. We explain surprising interactions of C++ features and poli- cies that sometimes complicate mixin implementations, while other times enable additional functionality without extra effort. 1 Introduction Large software artifacts are arguably among the most complex products of human intellect. The complexity of software has led to implementation methodologies that divide a problem into manageable parts and compose the parts to form the final prod- uct. Several research efforts have argued that C++ templates (a powerful parameteriza- tion mechanism) can be used to perform this division elegantly. In particular, the work of VanHilst and Notkin [29][30][31] showed how one can implement collaboration-based (or role-based) designs using a certain templatized class pattern, known as a mixin class (or just mixin). Compared to other techniques (e.g., a straightforward use of application frameworks [17]) the VanHilst and Notkin method yields less redundancy and reusable components that reflect the structure of the design. At the same time, unnecessary dynamic binding can be eliminated, result- ing into more efficient implementations.
    [Show full text]
  • Comp 411 Principles of Programming Languages Lecture 19 Semantics of OO Languages
    Comp 411 Principles of Programming Languages Lecture 19 Semantics of OO Languages Corky Cartwright Mar 10-19, 2021 Overview I • In OO languages, OO data values (except for designated non-OO types) are special records [structures] (finite mappings from names to values). In OO parlance, the components of record are called members. • Some members of an object may be functions called methods. Methods take this (the object in question) as an implicit parameter. Some OO languages like Java also support static methods that do not depend on this; these methods have no implicit parameters. In efficient OO language implementations, method members are shared since they are the same for all instances of a class, but this sharing is an optimization in statically typed OO languages since the collection of methods in a class is immutable during program evaluation (computation). • A method (instance method in Java) can only be invoked on an object (the receiver, an implicit parameter). Additional parameters are optional, depending on whether the method expects them. This invocation process is called dynamic dispatch because the executed code is literally extracted from the object: the code invoked at a call site depends on the value of the receiver, which can change with each execution of the call. • A language with objects is OO if it supports dynamic dispatch (discussed in more detail in Overview II & III) and inheritance, an explicit taxonomy for classifying objects based on their members and class names where superclass/parent methods are inherited unless overridden. • In single inheritance, this taxonomy forms a tree; • In multiple inheritance, it forms a rooted DAG (directed acyclic graph) where the root class is the universal class (Object in Java).
    [Show full text]
  • Multiple Inheritance and the Resolution of Inheritance Conflicts
    JOURNAL OF OBJECT TECHNOLOGY Online at http://www.jot.fm. Published by ETH Zurich, Chair of Software Engineering ©JOT, 2005 Vol. 4, No.2, March-April 2005 The Theory of Classification Part 17: Multiple Inheritance and the Resolution of Inheritance Conflicts Anthony J H Simons, Department of Computer Science, University of Sheffield, Regent Court, 211 Portobello Street, Sheffield S1 4DP, UK 1 INTRODUCTION This is the seventeenth article in a regular series on object-oriented theory for non- specialists. Using a second-order λ-calculus model, we have previously modelled the notion of inheritance as a short-hand mechanism for defining subclasses by extending superclass definitions. Initially, we considered the inheritance of type [1] and implementation [2] separately, but later combined both of these in a model of typed inheritance [3]. By simplifying the short-hand inheritance expressions, we showed how these are equivalent to canonical class definitions. We also showed how classes derived by inheritance are type compatible with their superclass. Further aspects of inheritance have included method combination [4], mixin inheritance [5] and inheritance among generic classes [6]. Most recently, we re-examined the ⊕ inheritance operator [7], to show how extending a class definition (the intension of a class) has the effect of restricting the set of objects that belong to the class (the extension of the class). We also added a type constraint to the ⊕ operator, to restrict the types of fields that may legally be combined with a base class to yield a subclass. By varying the form of this constraint, we modelled the typing of inheritance in Java, Eiffel, C++ and Smalltalk.
    [Show full text]
  • Multiple Inheritance
    Multiple Inheritance [email protected] Text: Chapter11 and 21, Big C++ Multiple Inheritance • Inheritance discussed so far is Single Inheritance • If a class has only one super class, then it is Single Inheritance • C++, also support Multiple Inheritance , i.e., when a class has more than one parent class Multiple Inheritance • Some of examples are- – Faculty could be Alumnus and Employee in DIICTian scenario – Head-Engineering , needs to be Manager and Engineer both – A CustomerEmployee would be Employee (a Person too), and Customer (a Person too)– forms diamond inheritance Here is how we have multiple inheritance in C++ class C : public A, public B { } • In this case, C inherits from A and B both … “public” Example: Multiple Inheritance Consider Example given • What methods class C has? • What is their visibility in class C? • What data members class C has? • What is their visibility in class C? Example: Multiple Inheritance Issues in Multiple Inheritance : Name ambiguity Base classes A and B of C both has getX() method Issues in Multiple Inheritance : Diamond Inheritance • Class B1 and B2 inherits from L, and • D inherits from B1 and B2, both • Therefore, in D, L inherits twice • It brings in some issues, consider example on next slide • What data and function members C has? • What is their visibility? Issues in Multiple Inheritance : Diamond Inheritance • Class D has – two copies of data ax – Ambiguous method names getX(), getAX() • Two copies of same variable should be more critical Issues in multiple inheritance Virtual Inheritance • C++ addresses this issue by allowing such base (being inherited multiple times) class to be virtual base class • As a result all virtual occurrences of the class throughout the class hierarchy share one actual occurrence of it.
    [Show full text]
  • Object Oriented Perl: an Introduction
    Object Oriented Perl: An Introduction Object Oriented Perl: An Introduction Abram Hindle Department of Computer Science University of Victoria [email protected] July 13, 2004 Abram Hindle 1 Object Oriented Perl: An Introduction This Presentation • What am I going to cover? – OO Intro – Packages – References – Constructor – Attributes – Methods – Inheritance – Fun Stuff – Getting Help – Conclusions – References Abram Hindle 2 Object Oriented Perl: An Introduction OO Introduction • What are objects? – A combination of attributes and functions associated with those attributes. Objects can have state, identify and behaviors. You can execute actions associated with objects. e.g. A dog object could bark. Effectively objects are instances of Classes. • What are classes? – The definition or blueprint for an object. http://www.justpbinfo.com/techdocs/ooterms.asp Abram Hindle 3 Object Oriented Perl: An Introduction OO Introduction • Why use Object Oriented Programming – OOP helps us organize our code and split our problems up into smaller blocks. – OOP is the current dominant programming style. – OOP seems to be the best that we currently have in imperative programming. – With OOP we gain useful things like polymorphism, encapsulation and other big words/concepts. Abram Hindle 4 Object Oriented Perl: An Introduction Packages • What are Packages? – The main way code is organized in Perl is with packages. – Sample Package: ∗ package Name; use strict; #save us debugging time ...code... 1; # outdated, used for a return from a use. – More than 1 package can exist in a file. Usually packages are saved into .pm files like Name.pm Abram Hindle 5 Object Oriented Perl: An Introduction Packages • More Details... – Our Class Names will be the package name.
    [Show full text]
  • An Exemplar Based Smalltalk
    An Exemplar Based Smalltaik Will R. LaLonde, Dave A. Thomas and John R. Pugh School of Computer Science Carleton University Ottawa, Ontario, Canada KIS 5B6 Abstract Two varieties of object-oriented systems exist: one In this paper, we detail some of the Smalltalk deficiencies based on classes as in Smalltalk and another based on that are a direct result of its class based orientation and describe exemplars (or prototypicai objects) as in Act/l. By converting how a more general and flexible system is obtained by Smalltalk from a class based orientation to an exemplar base, changing its underlying organizational base from classes to independent instance hierarchies and class hierarchies can be exemplars. The work is relevant to the evolution of any provided. Decoupling the two hierarchies in this way enables object-oriented system including the Flavour system in Lisp the user's (logical) view of a data type to be separated from the [Weinreb 807, Loops [Bobrow 81], Trellis [O'Brien 857, and implementer's (physical) view. It permits the instances of a more conventional languages being retro-fitted with class to have a representation totally different from the object-oriented facilities; e.g., C [Cox 84], Pascal [Tesler 847, instances of a superclass. Additionally, it permits the notion of Forth [Duff84], and Prolog [Shapiro 83, Vaucber 867. multiple representations to be provided without the need to Exemplar based systems include Act/l[Lieberman 81, introduce specialized classes for each representation. In the Smallworld [Laffgl], Thinglab [Borning 827, and Actra context of multiple inheritance, it leads to a novel view of [Thomas 857.
    [Show full text]
  • A Foundation for Trait-Based Metaprogramming
    A foundation for trait-based metaprogramming John Reppy Aaron Turon University of Chicago {jhr, adrassi}@cs.uchicago.edu Abstract We present a calculus, based on the Fisher-Reppy polymorphic Scharli¨ et al. introduced traits as reusable units of behavior inde- trait calculus [FR03], with support for trait privacy, hiding and deep pendent of the inheritance hierarchy. Despite their relative simplic- renaming of trait methods, and a more granular trait typing. Our ity, traits offer a surprisingly rich calculus. Trait calculi typically in- calculus is more expressive (it provides new forms of conflict- clude operations for resolving conflicts when composing two traits. resolution) and more flexible (it allows after-the-fact renaming) In the existing work on traits, these operations (method exclusion than the previous work. Traits provide a useful mechanism for shar- and aliasing) are shallow, i.e., they have no effect on the body of the ing code between otherwise unrelated classes. By adding deep re- other methods in the trait. In this paper, we present a new trait sys- naming, our trait calculus supports sharing code between methods. tem, based on the Fisher-Reppy trait calculus, that adds deep oper- For example, the JAVA notion of synchronized methods can im- ations (method hiding and renaming) to support conflict resolution. plemented as a trait in our system and can be applied to multiple The proposed operations are deep in the sense that they preserve methods in the same class to produce synchronized versions. We any existing connections between the affected method and the other term this new use of traits trait-based metaprogramming.
    [Show full text]