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53-631: AppKit comprises a collection of Objective-C classes and protocols that can be used to build an application in OpenStep/Cocoa. These classes can also be used in Swift through its Objective-C bridge. Xcode has built-in functionality for developing a Cocoa application using AppKit, including the ability to visually design user interfaces with Interface Builder . It relies heavily on patterns like reference types , delegation , notifications , target–action , and model–view–controller . A sign of

106-403: A release message to self, and return nil to indicate that initialization failed. Any checking for such errors must only be performed after having called the superclass initialization to ensure that destroying the object will be done correctly. If a class has more than one initialization method, only one of them (the designated initializer ) needs to follow this pattern; others should call

159-566: A Swift -only declarative UI framework. Prior to macOS Catalina , macOS also supported Carbon , a UI framework derived from the Macintosh Toolbox . Of the more than 170 classes included in the Application Kit, the following classes form the core: Objective-C Objective-C is a high-level general-purpose , object-oriented programming language that adds Smalltalk -style message passing (messaging) to

212-520: A console. This also helps to make up for lack of titles at the launch of new systems, as users can pull from the previous console's library of games while developers transition to the new hardware. Moreover, studies in the mid-1990s found that even consumers who never play older games after purchasing a new system consider backward compatibility a highly desirable feature, valuing the mere ability to continue to play an existing collection of games even if they choose never to do so. Backward compatibility with

265-523: A corresponding implementation unless they are abstract . The Smalltalk-style programming as used in Objective-C allows messages to go unimplemented, with the method resolved to its implementation at runtime. For example, a message may be sent to a collection of objects, to which only some will be expected to respond, without fear of producing runtime errors. Message passing also does not require that an object be defined at compile time . An implementation

318-421: A few practical changes to existing tools. Specifically, they needed to support objects in a flexible manner, come supplied with a usable set of libraries , and allow for the code (and any resources needed by the code) to be bundled into one cross-platform format. Love and Cox eventually formed PPI to commercialize their product, which coupled an Objective-C compiler with class libraries. In 1986, Cox published

371-483: A manufacturer decides to stop supporting older hardware. Classic video games are a common example used when discussing the value of supporting older software. The cultural impact of video games is a large part of their continued success, and some believe ignoring backward compatibility would cause these titles to disappear. Backward compatibility also acts as a selling point for new hardware, as an existing player base can more affordably upgrade to subsequent generations of

424-479: A method ; one sends a message . This is unlike the Simula -style programming model used by C++ . The difference between these two concepts is in how the code referenced by the method or message name is executed. In a Simula-style language, the method name is in most cases bound to a section of code in the target class by the compiler. In Smalltalk and Objective-C, the target of a message is resolved at runtime, with

477-412: A name labeling the argument that is part of the method name, followed by a colon followed by the expected argument type in parentheses and the argument name. The label can be omitted. A derivative of the interface definition is the category , which allows one to add methods to existing classes. The interface only declares the class interface and not the methods themselves: the actual code is written in

530-492: A platform for custom programming. To circumvent the terms of the GPL , NeXT had originally intended to ship the Objective-C frontend separately, allowing the user to link it with GCC to produce the compiler executable. Though initially accepted by Richard M. Stallman , this plan was rejected after Stallman consulted with GNU's lawyers and NeXT agreed to make Objective-C part of GCC. The work to extend GNU Compiler Collection (GCC)

583-452: A system. Modifying a system in a way that does not allow backward compatibility is sometimes called " breaking " backward compatibility. Such breaking usually incurs various types of costs, such as switching cost . A complementary concept is forward compatibility ; a design that is forward-compatible usually has a roadmap for compatibility with future standards and products. A simple example of both backward and forward compatibility

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636-479: Is a general notion of interoperation between software pieces that will not produce any errors when its functionality is invoked via API . The software is considered stable when its API that is used to invoke functions is stable across different versions. In operating systems, upgrades to newer versions are said to be backward compatible if executables and other files from the previous versions will work as usual. In compilers , backward compatibility may refer to

689-506: Is a list of methods that a class can opt to implement. It is specified in the documentation, since it has no presence in the language. Informal protocols are implemented as a category (see below) on NSObject and often include optional methods, which, if implemented, can change the behavior of a class. For example, a text field class might have a delegate that implements an informal protocol with an optional method for performing auto-completion of user-typed text. The text field discovers whether

742-535: Is based on OpenStep interface objects and is the most significant Objective-C environment being used for active development. At WWDC 2014, Apple introduced a new language, Swift , which was characterized as "Objective-C without the C". Objective-C is a thin layer atop C and is a "strict superset " of C, meaning that it is possible to compile any C program with an Objective-C compiler and to freely include C language code within an Objective-C class. Objective-C derives its object syntax from Smalltalk . All of

795-489: Is named objc_msg_sendv , but it has been deprecated in favor of a modern lookup system under objc_msg_lookup . Both styles of programming have multiple strengths and weaknesses. Object-oriented programming in the Simula ( C++ ) style allows multiple inheritance and faster execution by using compile-time binding whenever possible, but it does not support dynamic binding by default. It also forces all methods to have

848-418: Is never an allocated object that hasn't undergone initialization (and because it is unwise to keep the intermediate result since -init can return a different object than that on which it is called). Instantiation with the default, no-parameter initializer: Instantiation with a custom initializer: In the case where no custom initialization is being performed, the "new" method can often be used in place of

901-488: Is not necessarily known at link time which method will be called because the class of the receiver (the object being sent the message) need not be known until runtime. Once an Objective-C class is written, it can be instantiated. This is done by first allocating an uninitialized instance of the class (an object) and then by initializing it. An object is not fully functional until both steps have been completed. These steps should be accomplished with one line of code so that there

954-534: Is particularly important in computer instruction set architectures , two of the most successful being the IBM 360 / 370 / 390 / Zseries families of mainframes, and the Intel x86 family of microprocessors . IBM announced the first 360 models in 1964 and has continued to update the series ever since, with migration over the decades from 32-bit register/24-bit addresses to 64-bit registers and addresses. Intel announced

1007-449: Is still required for the method to be called in the derived object. (See the dynamic typing section below for more advantages of dynamic (late) binding.) Objective-C requires that the interface and implementation of a class be in separately declared code blocks. By convention, developers place the interface in a header file and the implementation in a code file. The header files, normally suffixed .h, are similar to C header files while

1060-466: Is the introduction of FM radio in stereo . FM radio was initially mono , with only one audio channel represented by one signal . With the introduction of two-channel stereo FM radio, many listeners had only mono FM receivers. Forward compatibility for mono receivers with stereo signals was achieved by sending the sum of both left and right audio channels in one signal and the difference in another signal. That allows mono FM receivers to receive and decode

1113-424: Is to refer to an instance method, with the class and then method names appended and colons changed to underscores. As the order of parameters is part of the method name, it cannot be changed to suit coding style or expression as with true named parameters. However, internal names of the function are rarely used directly. Generally, messages are converted to function calls defined in the Objective-C runtime library. It

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1166-477: The C programming language. Originally developed by Brad Cox and Tom Love in the early 1980s, it was selected by NeXT for its NeXTSTEP operating system . Due to Apple macOS ’s direct lineage from NeXTSTEP, Objective-C was the standard language used, supported, and promoted by Apple for developing macOS and iOS applications (via their respective application programming interfaces ( APIs ), Cocoa and Cocoa Touch ) from 1997, when Apple purchased NeXT until

1219-542: The receiver — is not guaranteed to respond to a message, and if it does not, it raises an exception. Sending the message method to the object pointed to by the pointer obj would require the following code in C++ : In Objective-C, this is written as follows: The "method" call is translated by the compiler to the objc_msgSend(id self, SEL op, ...) family of runtime functions. Different implementations handle modern additions like super . In GNU families this function

1272-514: The NeXTSTEP heritage, AppKit's classes and protocols still use the "NS" prefix. Most of the applications bundled with macOS—for example, the Finder , TextEdit , Calendar , and Preview —use AppKit to provide their user interface. macOS , iOS , iPadOS , and tvOS also support other UI frameworks, including UIKit , which is derived from AppKit and uses many similar structures, and SwiftUI ,

1325-878: The Objective-C frontend to Clang . The GNU project started work on its free software implementation of Cocoa , named GNUstep , based on the OpenStep standard. Dennis Glatting wrote the first GNU Objective-C runtime in 1992. The current GNU Objective-C runtime, in use since 1993, is the one developed by Kresten Krab Thorup while he was a university student in Denmark . Thorup also worked at NeXT from 1993 to 1996. After acquiring NeXT in 1996, Apple Computer used OpenStep in its then-new operating system, Mac OS X . This included Objective-C, NeXT's Objective-C-based developer tool, Project Builder , and its interface design tool, Interface Builder . Both were later merged into one application, Xcode . Most of Apple's current Cocoa API

1378-675: The Objective-C trademark) and extended the GCC compiler to support Objective-C. NeXT developed the Application Kit (AppKit) and Foundation Kit libraries on which the NeXTSTEP user interface and Interface Builder were based. While the NeXT workstations failed to make a great impact in the marketplace, the tools were widely lauded in the industry. NeXT dropped hardware production and focused on software tools, selling NeXTSTEP (and OPENSTEP) as

1431-491: The abilities of Smalltalk . He soon had a working implementation of an object-oriented extension to the C language, which he named Object-Oriented Pre-Compiler (OOPC). Love was hired by Schlumberger Research in 1982 and had the opportunity to acquire the first commercial copy of Smalltalk-80, which further influenced the development of their brainchild. To demonstrate that real progress could be made, Cox showed that making interchangeable software components really needed only

1484-471: The ability of a compiler for a newer version of the language to accept source code of programs or data that worked under the previous version. A data format is said to be backward compatible when a newer version of the program can open it without errors just like its predecessor. There are several incentives for a company to implement backward compatibility. Backward compatibility can be used to preserve older software that would have otherwise been lost when

1537-428: The alloc-init messages: Also, some classes implement class method initializers. Like +new , they combine +alloc and -init , but unlike +new , they return an autoreleased instance. Some class method initializers take parameters: The alloc message allocates enough memory to hold all the instance variables for an object, sets all the instance variables to zero values, and turns the memory into an instance of

1590-466: The class; at no point during the initialization is the memory an instance of the superclass. The init message performs the set-up of the instance upon creation. The init method is often written as follows: In the above example, notice the id return type. This type stands for pointer to any object in Objective-C (See the Dynamic typing section). The initializer pattern is used to assure that

1643-474: The delegate implements that method (via reflective programming (reflection)) and, if so, calls the delegate's method to support the auto-complete feature. Backward compatibility In telecommunications and computing , backward compatibility (or backwards compatibility ) is a property of an operating system , software, real-world product, or technology that allows for interoperability with an older legacy system , or with input designed for such

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1696-639: The designated initializer instead of the superclass initializer. In other programming languages, these are called interfaces . Objective-C was extended at NeXT to introduce the concept of multiple inheritance of specification, but not implementation, through the introduction of protocols . This is a pattern achievable either as an abstract multiple inherited base class in C++ , or as an interface (as in Java and C# ). Objective-C makes use of ad hoc protocols called informal protocols and compiler-enforced protocols called formal protocols . An informal protocol

1749-513: The first Intel 8086 / 8088 processors in 1978, again with migrations over the decades from 16-bit to 64-bit. (The 8086/8088, in turn, were designed with easy machine-translatability of programs written for its predecessor in mind, although they were not instruction-set compatible with the 8-bit Intel 8080 processor of 1974. The Zilog Z80 , however, was fully backward compatible with the Intel 8080.) Fully backward compatible processors can process

1802-448: The form: In the above, plus signs denote class methods , or methods that can be called on the class itself (not on an instance), and minus signs denote instance methods , which can only be called on a particular instance of the class. Class methods also have no access to instance variables . The code above is roughly equivalent to the following C++ interface: Note that instanceMethod2With2Parameters:param2_callName: demonstrates

1855-443: The implementation (method) files, normally suffixed .m, can be very similar to C code files. This is analogous to class declarations as used in other object-oriented languages, such as C++ or Python. The interface of a class is usually defined in a header file. A common convention is to name the header file after the name of the class, e.g. Ball.h would contain the interface for the class Ball . An interface declaration takes

1908-533: The implementation file. Implementation (method) files normally have the file extension .m , which originally signified "messages". Methods are written using their interface declarations. Comparing Objective-C and C: The syntax allows pseudo- naming of arguments . Internal representations of a method vary between different implementations of Objective-C. If myColor is of the class Color , instance method -changeColorToRed:green:blue: might be internally labeled _i_Color_changeColorToRed_green_blue . The i

1961-499: The interleaving of selector segments with argument expressions, for which there is no direct equivalent in C/C++. Return types can be any standard C type, a pointer to a generic Objective-C object, a pointer to a specific type of object such as NSArray *, NSImage *, or NSString *, or a pointer to the class to which the method belongs (instancetype). The default return type is the generic Objective-C type id . Method arguments begin with

2014-442: The introduction of the Swift language in 2014. Objective-C programs developed for non-Apple operating systems or that are not dependent on Apple's APIs may also be compiled for any platform supported by GNU GNU Compiler Collection (GCC) or LLVM / Clang . Objective-C source code 'messaging/implementation' program files usually have .m filename extensions, while Objective-C 'header/interface' files have .h extensions,

2067-664: The main CPU for PS1 mode or upclocking itself to offload I/O in PS2 mode. This coprocessor was replaced with a PowerPC -based processor in later systems to serve the same functions, emulating the PS1 CPU core. Such an approach can backfire, though, as was the case of the Super Nintendo Entertainment System (Super NES). It opted for the more peculiar 65C816 CPU over the more popular 16-bit microprocessors on

2120-409: The main description of Objective-C in its original form in the book Object-Oriented Programming, An Evolutionary Approach . Although he was careful to explain that there is more to the problem of reusability than just what Objective-C provides, the language was often compared feature for feature with other languages. In 1988, NeXT licensed Objective-C from StepStone (the new name of PPI, the owner of

2173-431: The new system. Because of this, several console manufacturers phased out backward compatibility towards the end of the console generation in order to reduce cost and briefly reinvigorate sales before the arrival of newer hardware. It is possible to bypass some of these hardware costs. For instance, earlier PlayStation 2 (PS2) systems used the core of the original PlayStation (PS1) CPU as a dual-purpose processor, either as

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2226-492: The newest generation of consoles such as PlayStation 5 and Xbox Series X/S also support this feature. A large part of the success and implementation of this feature is that the hardware within newer generation consoles is both powerful and similar enough to legacy systems that older titles can be broken down and re-configured to run on the Xbox One. This program has proven incredibly popular with Xbox players and goes against

2279-450: The object is properly initialized by its superclass before the init method performs its initialization. It performs the following actions: A non-valid object pointer has the value nil ; conditional statements like if treat nil like a null pointer, so the initialization code will not be executed if [super init] returned nil. If there is an error in initialization the init method should perform any necessary cleanup, including sending

2332-497: The original PlayStation (PS) software discs and peripherals is considered to have been a key selling point for the PlayStation 2 (PS2) during its early months on the market. Despite not being included at launch, Microsoft slowly incorporated backward compatibility for select titles on the Xbox One several years into its product life cycle. Players have racked up over a billion hours with backward-compatible games on Xbox, and

2385-423: The product that may lead to longer time to market , technological hindrances, and slowing innovation; and increased expectations from users in terms of compatibility. It also introduces the risk that developers will favor developing games that are compatible with both the old and new systems, since this gives them a larger base of potential buyers, resulting in a dearth of software which uses the advanced features of

2438-409: The receiving object itself interpreting the message. A method is identified by a selector or SEL — a unique identifier for each message name, often just a NUL -terminated string representing its name — and resolved to a C method pointer implementing it: an IMP . A consequence of this is that the message-passing system has no type checking. The object to which the message is directed —

2491-424: The recent trend of studio-made remasters of classic titles, creating what some believe to be an important shift in console makers' strategies. The monetary costs of supporting old software is considered a large drawback to the usage of backward compatibility. The associated costs of backward compatibility are a larger bill of materials if hardware is required to support the legacy systems; increased complexity of

2544-494: The same binary executable software instructions as their predecessors, allowing the use of a newer processor without having to acquire new applications or operating systems . Similarly, the success of the Wi-Fi digital communication standard is attributed to its broad forward and backward compatibility; it became more popular than other standards that were not backward compatible. In software development, backward compatibility

2597-453: The same as C header files. Objective-C++ files are denoted with a .mm file extension. Objective-C was created mainly by Brad Cox and Tom Love in the early 1980s at their company Productivity Products International (PPI) . Leading up to the creation of their company, both had been introduced to Smalltalk while at ITT Corporation 's Programming Technology Center in 1981. The earliest work on Objective-C traces back to around then. Cox

2650-444: The sum signal while ignoring the difference signal, which is necessary only for separating the audio channels. Stereo FM receivers can receive a mono signal and decode it without the need for a second signal, and they can separate a sum signal to left and right channels if both sum and difference signals are received. Without the requirement for backward compatibility, a simpler method could have been chosen. Full backward compatibility

2703-415: The syntax for non-object-oriented operations (including primitive variables, pre-processing, expressions, function declarations, and function calls) are identical to those of C, while the syntax for object-oriented features is an implementation of Smalltalk-style messaging. The Objective-C model of object-oriented programming is based on message passing to object instances. In Objective-C one does not call

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2756-462: Was intrigued by problems of true reusability in software design and programming. He realized that a language like Smalltalk would be invaluable in building development environments for system developers at ITT. However, he and Tom Love also recognized that backward compatibility with C was critically important in ITT's telecom engineering milieu. Cox began writing a pre-processor for C to add some of

2809-420: Was led by Steve Naroff, who joined NeXT from StepStone. The compiler changes were made available as per GNU General Public License (GPL) terms, but the runtime libraries were not, rendering the open source contribution unusable to the general public. This led to other parties developing such runtime libraries under open source licenses. Later, Steve Naroff was also principal contributor to work at Apple to build

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