Exploring Self: A Prototype-Based Object-Oriented Programming Language
Self is a unique and influential programming language that has garnered attention for its innovative approach to object-oriented design. Originating as a dialect of Smalltalk, it made significant strides in the realm of object-oriented programming (OOP), with particular emphasis on prototypes as opposed to the more conventional class-based inheritance models. First developed in the 1980s and 1990s, Self has evolved into a fascinating study of how language design can be informed by both theoretical innovation and practical performance challenges.
Origins and Development
Self was created by David Ungar and his collaborators at Sun Microsystems, and it became an important part of experimental programming language research during the 1980s. The language’s development was heavily influenced by Smalltalk, a language already known for its commitment to object-oriented principles. However, unlike Smalltalk, which relies on classes to define the structure of objects, Self adopted a prototype-based approach to object creation and inheritance. This shift to prototype-based programming represents a core distinction between Self and more traditional object-oriented languages.
Prototype-based programming, as implemented in Self, removes the need for classes. Instead, objects themselves act as templates for other objects, allowing for inheritance and behavior sharing directly through prototypes. In essence, each object is capable of becoming a prototype for others, providing a highly flexible and dynamic model for organizing code.
Core Features of Self
The most significant feature of Self is its prototype-based object system. Unlike the class-based model, where classes define the blueprint for creating objects, Self allows objects to clone themselves and serve as prototypes for others. This fundamental distinction allows greater flexibility in object creation and modification. In Self, each object can be directly altered, and its behavior can be dynamically adjusted through prototypes, which is a key departure from traditional object-oriented programming (OOP) paradigms.
Another important feature is Self’s emphasis on simplicity and minimalism. The language is deliberately kept small, which encourages clean and efficient designs. Its syntax is designed to be highly readable and intuitive, reducing the learning curve for developers while still maintaining powerful capabilities.
Additionally, Self employs just-in-time (JIT) compilation to optimize performance. While many high-level programming languages suffer from performance bottlenecks due to their abstraction layers, Self was designed to address this problem by implementing JIT compilation techniques that allow the language to execute very efficiently—often achieving performance close to that of low-level languages like C.
Prototype-Based Inheritance
At the heart of Self’s design lies the concept of prototype-based inheritance. In this model, objects themselves serve as prototypes, which can be cloned and modified by other objects. Instead of the class-based inheritance model, where a subclass inherits from a class, Self allows an object to inherit directly from another object, using the prototype as a template.
This distinction means that in Self, the concept of “inheritance” is much more dynamic and flexible than in class-based systems. An object can inherit properties and behaviors from multiple prototypes, allowing for a much more fluid and adaptive design. Furthermore, it allows for more fine-grained control over object behavior, as prototypes can be modified at runtime.
Prototype-based inheritance is highly advantageous when dealing with systems that require flexibility and adaptability, such as interactive applications and systems where objects may evolve or change during runtime. This dynamic nature allows developers to write more expressive and adaptable code while retaining a simple and elegant structure.
Performance Innovations and JIT Compilation
One of the major achievements of Self lies in its performance optimizations, particularly through its use of Just-In-Time (JIT) compilation. Unlike many interpreted languages, which suffer from slower execution speeds, Self’s JIT compiler enables it to run at a speed comparable to that of compiled languages like C.
This development was particularly significant in the 1990s when Self’s performance capabilities became an important benchmark for virtual machine (VM) optimization techniques. Much of the innovation that went into Self’s JIT compilation techniques was later adopted by Sun Microsystems for the HotSpot VM used in Java. By pushing the limits of just-in-time compilation, Self helped to advance the state of the art in dynamic language performance.
In the process of developing these performance features, the team behind Self not only addressed theoretical challenges but also ensured that the language could be used in practical, performance-sensitive applications. The result was a system that could execute complex object-oriented code efficiently, even in scenarios where performance would typically be a concern.
Self’s Influence on Modern Programming Languages
Self’s impact on the world of programming languages, though not as widely known as some of its peers, has been profound. Many of the ideas introduced in Self have since been incorporated into other major programming languages. The prototype-based inheritance model, for example, influenced languages such as JavaScript, which now uses prototypes as the basis for object inheritance.
Self also had a direct influence on the development of Smalltalk, particularly in its experimental use of JIT compilation. This later influenced the design of Java’s HotSpot virtual machine, as Sun Microsystems recognized the potential of Self’s approach to improving performance in dynamically-typed, object-oriented languages.
In addition to its influence on JavaScript and Java, Self has also informed various other experimental languages and research projects. The simplicity of its design and the elegance of its prototype-based inheritance system continue to serve as a model for modern language designers seeking to create more flexible, adaptable, and high-performance object-oriented languages.
Klein Project and the Future of Self
While Self’s development was primarily active during the 1980s and 1990s, it continues to have a presence in the academic and research communities. In 2006, the Klein project was launched, an ambitious effort to implement a Self virtual machine entirely in the Self language. This project is a testament to the enduring relevance of Self in the world of programming language design.
The Klein project sought to explore Self’s potential for further optimization and to better understand how a language like Self could be used to implement its own virtual machine. This research pushed the boundaries of what was possible in terms of self-hosting virtual machines and demonstrated the ongoing relevance of Self in the study of programming language architecture.
The last official release of Self came in 2017 with version 2017.1, though development has slowed in recent years. Despite this, Self remains a critical point of reference for developers and researchers exploring object-oriented programming, language design, and performance optimization.
Conclusion
Self represents a significant milestone in the evolution of object-oriented programming languages. By pioneering the prototype-based approach to object design, Self introduced new ways of thinking about inheritance, object creation, and code organization. Its emphasis on simplicity, flexibility, and performance through just-in-time compilation has left a lasting legacy on both the academic and practical realms of programming language design.
While it may not have reached the widespread adoption of languages like Java or Python, Self’s contributions to the programming world are undeniable. From influencing the development of JavaScript and Java to its cutting-edge performance optimizations, Self’s impact is felt far beyond its relatively niche status. It remains an important area of study for anyone interested in the history and future of object-oriented languages, and its prototype-based inheritance system continues to inspire new generations of programming language designers.
For further exploration of Self, you can visit the official website at selflanguage.org or read more about its history and features on its Wikipedia page.