This overview of C++ presents the key design, programming, and language-technical concepts using examples to give the reader a feel for the language. C++ is a general-purpose programming language with a bias towards systems programming that supports efficient low-level computation, data abstraction, object-oriented programming, and generic programming. 1

This thesis defines a set of program restructuring operations (refactorings) that support the design, evolution and reuse of object-oriented application frameworks. The focus of the thesis is on automating the refactorings in a way that preserves the behavior of a program. The refactorings are defined to be behavior preserving, provided that their preconditions are met. Most of the refactorings are simple to implement and it is almost trivial to show that they are behavior preserving. However, for a few refactorings, one or more of their preconditions are in general undecidable. Fortunately, for some cases it can be determined whether these refactorings can be applied safely. Three of the most complex refactorings are defined in detail: generalizing the inheritance hierarchy, specializing the inheritance hierarchy and using aggregations to model the relationships among classes. These operations are decomposed into more primitive parts, and the power of these operations is discussed from the perspectives of automatability and usefulness in supporting design. Two design constraints needed in refactoring are class invariants and exclusive components. These constraints are needed to ensure that behavior is preserved across some refactorings. This thesis gives some conservative algorithms for determining whether a program satisfies these constraints, and describes how to use this design information to refactor a program.

Object-oriented programming languages allow inter-object aliasing. Although necessary to construct linked data structures and networks of interacting objects, aliasing is problematic in that an aggregate object's state can change via an alias to one of its components, without the aggregate being aware of any aliasing. Ownership types form a static type system that indicates object ownership. This provides a flexible mechanism to limit the visibility of object references and restrict access paths to objects, thus controlling a system's dynamic topology. The type system is shown to be sound, and the specific aliasing properties that a system's object graph satisfies are formulated and proven invariant for well-typed programs. Keywords Alias protection, sharing, containment, ownership, representation exposure, programming language design 1

This paper proposes a framework for constructing an operating system in an open and mobile computing environment. The framework provides object/metaobject separation and metahierarchy. In the framework, we view object migration as a basic mechanism to accommodate object heterogeneity. The relevance of the proposed framework to existing system structures is discussed. We then present a practical implementation of the Apertos operating system in this framework, where reflectors are introduced for metaobject programming and MetaCore for providing common primitives. We present some evaluation results of the Apertos operating system. We also present related work in terms of reflection mechanisms and systems.

In the past, object-oriented language designers and programmers have been forced to choose between pure message passing and performance. Last year, our SELF system achieved close to half the speed of optimized C but suffered from impractically long compile times. Two new optimization techniques, deferred compilation of uncommon cases and non-backtracking splitting using path objects, have improved compilation speed by more than an order of magnitude. SELF now compiles about as fast as an optimizing C compiler and runs at over half the speed of optimized C. This new level of performance may make pure object-oriented languages practical. 1 Introduction In the past, object-oriented language designers and programmers have been forced to choose between purity and performance. In a pure object-oriented language, all computation, even low-level operations like variable accessing, arithmetic, and array indexing, is performed by sending messages to objects. Although a message send may cost o...

Cecil is a new purely object-oriented language intended to support rapid construction of highquality, extensible software. Cecil combines multi-methods with a classless object model, object-based encapsulation, and optional static type checking. Cecil's static type system distinguishes between subtyping and code inheritance, but Cecil enables these two graphs to be described with a single set of declarations, optimizing the common case where the two graphs are parallel. Cecil includes a fairly flexible form of parameterization, including both explicitly parameterized objects, types, and methods and implicitly parameterized methods related to the polymorphic functions commonly found in functional languages. By making type declarations optional, Cecil aims to support mixed exploratory and production programming styles. This document describes the design of the Cecil language as of March, 1993. It mixes the specification of the language with discussions of design issues and explanations of...

Abstract. We have developed and implemented techniques that double the performance of dynamically-typed object-oriented languages. Our SELF implementation runs twice as fast as the fastest Smalltalk implementation, despite SELF’s lack of classes and explicit variables. To compensate for the absence of classes, our system uses implementation-level maps to transparently group objects cloned from the same prototype, providing data type information and eliminating the apparent space overhead for prototype-based systems. To compensate for dynamic typing, user-defined control structures, and the lack of explicit variables, our system dynamically compiles multiple versions of a source method, each customized according to its receiver’s map. Within each version the type of the receiver is fixed, and thus the compiler can statically bind and inline all messages sent to self. Message splitting and type prediction extract and preserve even more static type information, allowing the compiler to inline many other messages. Inlining dramatically improves performance and eliminates the need to hard-wire low-level methods such as +, ==, and ifTrue:. Despite inlining and other optimizations, our system still supports interactive programming environments. The system traverses internal dependency lists to invalidate all compiled methods

Object-oriented programming languages confer many benefits, including abstraction, which lets the programmer hide the details of an object’s implementation from the object’s clients. Unfortunately, crossing abstraction boundaries often incurs a substantial run-time overhead in the form of frequent procedure calls. Thus, pervasive use of abstraction, while desirable from a design standpoint, may be impractical when it leads to inefficient programs. Aggressive compiler optimizations can reduce the overhead of abstraction. However, the long compilation times introduced by optimizing compilers delay the programming environment‘s responses to changes in the program. Furthermore, optimization also conflicts with source-level debugging. Thus, programmers are caught on the horns of two dilemmas: they have to choose between abstraction and efficiency, and between responsive programming environments and efficiency. This dissertation shows how to reconcile these seemingly contradictory goals by performing optimizations lazily. Four new techniques work together to achieve high performance and high responsiveness: • Type feedback achieves high performance by allowing the compiler to inline message sends based on information extracted from the runtime system. On average, programs run 1.5 times faster than the previous SELF system; compared to a commercial Smalltalk implementation, two medium-sized benchmarks run about three times faster. This level of performance is obtained with a compiler that is both simpler and faster than previous SELF compilers. • Adaptive optimization achieves high responsiveness without sacrificing performance by using a fast nonoptimizing compiler to generate initial code while automatically recompiling heavily used parts of the program with an optimizing compiler. On a previous-generation workstation like the SPARCstation-2, fewer than 200 pauses exceeded 200 ms during a 50-minute interaction, and 21 pauses exceeded one second. On a currentgeneration workstation, only 13 pauses exceed 400 ms. • Dynamic deoptimization shields the programmer from the complexity of debugging optimized code by transparently recreating non-optimized code as needed. No matter whether a program is optimized or not, it can always be stopped, inspected, and single-stepped. Compared to previous approaches, deoptimization allows more debugging while placing fewer restrictions on the optimizations that can be performed. • Polymorphic inline caching generates type-case sequences on-the-fly to speed up messages sent from the same call site to several different types of object. More significantly, they collect concrete type information for the optimizing compiler. With better performance yet good interactive behavior, these techniques make exploratory programming possible both for pure object-oriented languages and for application domains requiring higher ultimate performance, reconciling exploratory programming, ubiquitous abstraction, and high performance.

this paper, we introduce the ANTLR (ANother Tool for Language Recognition) parser generator, which addresses all these issues. ANTLR is a component of the Purdue Compiler Construction Tool Set (PCCTS)

Wrappers are mechanisms for introducing new behavior that is executed before and/or after, and perhaps even in lieu of, an existing method. This paper examines several ways to implement wrappers in Smalltalk, and compares their performance. Smalltalk programmers often use Smalltalk's lookup failure mechanism to customize method lookup. Our focus is different. Rather than changing the method lookup process, we modify the method objects that the lookup process returns. We call these objects method wrappers.Wehaveused method wrappers to construct several program analysis tools: a coverage tool, a class collaboration tool, and an interaction diagramming tool. We also show how we used method wrappers to construct several extensions to Smalltalk: synchronized methods, assertions, and multimethods. Wrappers are relatively easy to build in Smalltalk because it was designed with reflective facilities that allow programmers to intervene in the lookup process. Other languages differ in the degree to which they can accommodate change. Our experience testifies to the value, power, and utility of openness.