In the s, object-oriented programming was put into practice with the Simula language, which introduced important concepts that are today an essential part of object-oriented programming, such as class and object , inheritance, and dynamic binding. For programming security purposes a detection process was implemented so that through reference counts a last resort garbage collector deleted unused objects in the random-access memory RAM.
In , Kristen Nygaard initiated a project for a simulation language at the Norwegian Computing Center , based on his previous use of the Monte Carlo simulation and his work to conceptualise real-world systems.
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Simula launched in , and was promoted by Dahl and Nygaard throughout and , leading to increasing use of the programming language in Sweden, Germany and the Soviet Union. In , the language became widely available through the Burroughs B computers , and was later also implemented on the URAL computer.
In , Dahl and Nygaard wrote a Simula compiler. They settled for a generalised process concept with record class properties, and a second layer of prefixes. Through prefixing a process could reference its predecessor and have additional properties. Simula thus introduced the class and subclass hierarchy, and the possibility of generating objects from these classes. The Simula 1 compiler and a new version of the programming language, Simula 67, was introduced to the wider world through the research paper "Class and Subclass Declarations" at a conference. By , the Association of Simula Users had members in 23 different countries.
Early a Simula 67 compiler was released free of charge for the DECsystem mainframe family. The object-oriented Simula programming language was used mainly by researchers involved with physical modelling , such as models to study and improve the movement of ships and their content through cargo ports. Smaltalk included a programming environment and was dynamically typed , and at first was interpreted , not compiled.
Smalltalk got noted for its application of object orientation at the language level and its graphical development environment. Smalltalk went through various versions and interest in the language grew. In the s, Smalltalk influenced the Lisp community to incorporate object-based techniques that were introduced to developers via the Lisp machine. Experimentation with various extensions to Lisp such as LOOPS and Flavors introducing multiple inheritance and mixins eventually led to the Common Lisp Object System , which integrates functional programming and object-oriented programming and allows extension via a Meta-object protocol.
In the s, there were a few attempts to design processor architectures that included hardware support for objects in memory but these were not successful. In , Goldberg edited the August issue of Byte Magazine , introducing Smalltalk and object-oriented programming to a wider audience. Focused on software quality, Eiffel is a purely object-oriented programming language and a notation supporting the entire software lifecycle.
Meyer described the Eiffel software development method, based on a small number of key ideas from software engineering and computer science, in Object-Oriented Software Construction. Essential to the quality focus of Eiffel is Meyer's reliability mechanism, Design by Contract , which is an integral part of both the method and language.
Introduction to the C# Language and the .NET Framework
In the early and mids object-oriented programming developed as the dominant programming paradigm when programming languages supporting the techniques became widely available. These included Visual FoxPro 3. Its dominance was further enhanced by the rising popularity of graphical user interfaces , which rely heavily upon object-oriented programming techniques. OOP toolkits also enhanced the popularity of event-driven programming although this concept is not limited to OOP.
Modula-2 included both, and their succeeding design, Oberon , included a distinctive approach to object orientation, classes, and such. Adding these features to languages that were not initially designed for them often led to problems with compatibility and maintainability of code. More recently, a number of languages have emerged that are primarily object-oriented, but that are also compatible with procedural methodology.
Two such languages are Python and Ruby. Probably the most commercially important recent object-oriented languages are Java , developed by Sun Microsystems , as well as C and Visual Basic. NET VB. NET , both designed for Microsoft's. NET platform. Each of these two frameworks shows, in its own way, the benefit of using OOP by creating an abstraction from implementation. NET and C support cross-language inheritance, allowing classes defined in one language to subclass classes defined in the other language. Simula is generally accepted as being the first language with the primary features of an object-oriented language.
It was created for making simulation programs , in which what came to be called objects were the most important information representation.
Chapter 2: Type Members | C# Class Design Handbook: Coding Effective Classes
Smalltalk to is another early example, and the one with which much of the theory of OOP was developed. Concerning the degree of object orientation, the following distinctions can be made:. In recent years, object-oriented programming has become especially popular in dynamic programming languages.
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Another scripting language that takes this approach is Lua. The messages that flow between computers to request services in a client-server environment can be designed as the linearizations of objects defined by class objects known to both the client and the server.
For example, a simple linearized object would consist of a length field, a code point identifying the class, and a data value.
A more complex example would be a command consisting of the length and code point of the command and values consisting of linearized objects representing the command's parameters. Each such command must be directed by the server to an object whose class or superclass recognizes the command and is able to provide the requested service.
Clients and servers are best modeled as complex object-oriented structures. Distributed Data Management Architecture DDM took this approach and used class objects to define objects at four levels of a formal hierarchy:.
The initial version of DDM defined distributed file services. Challenges of object-oriented design are addressed by several approaches. Most common is known as the design patterns codified by Gamma et al. More broadly, the term " design patterns " can be used to refer to any general, repeatable, solution pattern to a commonly occurring problem in software design. Some of these commonly occurring problems have implications and solutions particular to object-oriented development.
It is intuitive to assume that inheritance creates a semantic " is a " relationship, and thus to infer that objects instantiated from subclasses can always be safely used instead of those instantiated from the superclass. This intuition is unfortunately false in most OOP languages, in particular in all those that allow mutable objects.
Subtype polymorphism as enforced by the type checker in OOP languages with mutable objects cannot guarantee behavioral subtyping in any context. Behavioral subtyping is undecidable in general, so it cannot be implemented by a program compiler. Class or object hierarchies must be carefully designed, considering possible incorrect uses that cannot be detected syntactically. This issue is known as the Liskov substitution principle. Along with exploring the capabilities and pitfalls of object-oriented programming, it describes 23 common programming problems and patterns for solving them.
As of April , the book was in its 36th printing. Both object-oriented programming and relational database management systems RDBMSs are extremely common in software today [update]. Since relational databases don't store objects directly though some RDBMSs have object-oriented features to approximate this , there is a general need to bridge the two worlds. The problem of bridging object-oriented programming accesses and data patterns with relational databases is known as object-relational impedance mismatch.
There are a number of approaches to cope with this problem, but no general solution without downsides. OOP can be used to associate real-world objects and processes with digital counterparts.
However, not everyone agrees that OOP facilitates direct real-world mapping see Criticism section or that real-world mapping is even a worthy goal; Bertrand Meyer argues in Object-Oriented Software Construction  that a program is not a model of the world but a model of some part of the world; "Reality is a cousin twice removed". At the same time, some principal limitations of OOP have been noted.
However, Niklaus Wirth who popularized the adage now known as Wirth's law : "Software is getting slower more rapidly than hardware becomes faster" said of OOP in his paper, "Good Ideas through the Looking Glass", "This paradigm closely reflects the structure of systems 'in the real world', and it is therefore well suited to model complex systems with complex behaviours"  contrast KISS principle.
OOP was developed to increase the reusability and maintainability of source code. With the increasing relevance of parallel hardware and multithreaded coding , developing transparent control flow becomes more important, something hard to achieve with OOP. Responsibility-driven design defines classes in terms of a contract, that is, a class should be defined around a responsibility and the information that it shares. This is contrasted by Wirfs-Brock and Wilkerson with data-driven design , where classes are defined around the data-structures that must be held.
The authors hold that responsibility-driven design is preferable. Luca Cardelli has claimed that OOP code is "intrinsically less efficient" than procedural code, that OOP can take longer to compile, and that OOP languages have "extremely poor modularity properties with respect to class extension and modification", and tend to be extremely complex.