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31-536: The project was founded by Hamilton Verissimo de Oliveira (aka "Hammett"), who was a member of the Apache Avalon and the Apache Excalibur projects. Keenly interested in the development of an inversion of control container, after he resigned from Avalon and became disillusioned with Excalibur, he went on to develop and release his own for the .NET platform. Hammett was joined by other developers after publishing

62-496: A framework consists of composing and subclassing the existing classes. The necessary functionality can be implemented by using the Template Method Pattern in which the frozen spots are known as invariant methods and the hot spots are known as variant or hook methods. The invariant methods in the superclass provide default behaviour while the hook methods in each subclass provide custom behaviour. When developing

93-635: A larger software platform to facilitate the development of software applications , products and solutions. Software frameworks may include support programs, compilers, code libraries, toolsets, and application programming interfaces (APIs) that bring together all the different components to enable development of a project or system . Frameworks have key distinguishing features that separate them from normal libraries : The designers of software frameworks aim to facilitate software developments by allowing designers and programmers to devote their time to meeting software requirements rather than dealing with

124-400: A menu item is selected. In the mail client example, the framework could follow both the keyboard and mouse inputs and call the command invoked by the user by either means and at the same time monitor the network interface to find out if new messages arrive and refresh the screen when some network activity is detected. The same framework could be used as the skeleton for a spreadsheet program or

155-464: A product. Further, due to the complexity of their APIs, the intended reduction in overall development time may not be achieved due to the need to spend additional time learning to use the framework; this criticism is clearly valid when a special or new framework is first encountered by development staff. If such a framework is not used in subsequent job taskings, the time invested in learning the framework can cost more than purpose-written code familiar to

186-588: A series of articles on Code Project , and the Castle Project eventually expanded its mission "to provide a simple set of tools to speed up the development of common enterprise and web applications while promoting good architecture". The Castle Project continues to gain acceptance and mind-share from the .NET community, including recognition from Microsoft thought leaders as a framework to assist with building "robust, extensible, working software". In 2006, Hammett started his own company to offer commercial support for

217-459: A text editor. Conversely, the framework knows nothing about Web browsers, spreadsheets, or text editors; implementing their functionality takes custom code. Inversion of control carries the strong connotation that the reusable code and the problem-specific code are developed independently even though they operate together in an application. Callbacks , schedulers , event loops , and the template method are examples of design patterns that follow

248-435: Is a design principle in which custom-written portions of a computer program receive the flow of control from an external source (e.g. a framework ). The term "inversion" is historical: a software architecture with this design "inverts" control as compared to procedural programming . In procedural programming, a program's custom code calls reusable libraries to take care of generic tasks, but with inversion of control, it

279-437: Is achieved by mechanisms such as dependency injection or a service locator . In IoC, the code could also be linked statically during compilation, but finding the code to execute by reading its description from external configuration instead of with a direct reference in the code itself. In dependency injection, a dependent object or module is coupled to the object it needs at run time . Which particular object will satisfy

310-449: Is implemented by class B ; the program instantiates A and B , and then injects B into A . Web browsers implement inversion of control for DOM events in HTML. The application developer uses document.addEventListener() to register a callback. This example code for an ASP.NET Core web application creates a web application host, registers an endpoint, and then passes control to

341-450: Is not a new term in computer science. Martin Fowler traces the etymology of the phrase back to 1988, but it is closely related to the concept of program inversion described by Michael Jackson in his Jackson Structured Programming methodology in the 1970s. A bottom-up parser can be seen as an inversion of a top-down parser : in the one case, the control lies with the parser, while in

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372-405: Is often implemented using IoC so that the custom code need only be concerned with the handling of events, while the event loop and dispatch of events/messages is handled by the framework or the runtime environment. In web server application frameworks, dispatch is usually called routing, and handlers may be called endpoints. The phrase "inversion of control" has separately also come to be used in

403-459: Is the external source or framework that calls the custom code. Inversion of control has been widely used by application development frameworks since the rise of GUI environments and continues to be used both in GUI environments and in web server application frameworks . Inversion of control makes the framework extensible by the methods defined by the application programmer. Event-driven programming

434-430: Is user-defined). For those frameworks that generate code, for example, "elegance" would imply the creation of code that is clean and comprehensible to a reasonably knowledgeable programmer (and which is therefore readily modifiable), versus one that merely generates correct code. The elegance issue is why relatively few software frameworks have stood the test of time: the best frameworks have been able to evolve gracefully as

465-547: The Castle Project and for the applications developed using the framework. In August 2008, he joined Microsoft as a Program Manager on the MEF team. On October 31, 2008, Hammett announced on his blog that the Castle Project had been split, and subsequently all subprojects would be maintained and released independently. The first project to be released after the split was DynamicProxy, on May 4, 2009. Inversion of control In software engineering , inversion of control ( IoC )

496-414: The common code of the enterprise, instead of using a generic "one-size-fits-all" framework developed by third parties for general purposes. An example of that would be how the user interface in such an application package as an office suite grows to have common look, feel, and data-sharing attributes and methods, as the once disparate bundled applications, grow unified into a suite that is tighter and smaller;

527-504: The community of Java programmers to refer specifically to the patterns of dependency injection (passing to objects the services they need) that occur with "IoC containers" in Java frameworks such as the Spring framework . In this different sense, "inversion of control" refers to granting the framework control over the implementations of dependencies that are used by application objects rather than to

558-448: The dependency during program execution typically cannot be known at compile time using static analysis . While described in terms of object interaction here, the principle can apply to other programming methodologies besides object-oriented programming . In order for the running program to bind objects to one another, the objects must possess compatible interfaces . For example, class A may delegate behavior to interface I which

589-440: The framework: Software framework In computer programming , a software framework is an abstraction in which software , providing generic functionality, can be selectively changed by additional user-written code, thus providing application-specific software. It provides a standard way to build and deploy applications and is a universal, reusable software environment that provides particular functionality as part of

620-406: The function call, and the main function uses this value to execute the associated command. This style was common in text-based interfaces . For example, an email client may show a screen with commands to load new mail, answer the current mail, create new mail, etc., and the program execution would block until the user presses a key to select a command. With inversion of control, on the other hand,

651-424: The inversion of control principle, although the term is most commonly used in the context of object-oriented programming . ( Dependency injection is an example of the separate, specific idea of "inverting control over the implementations of dependencies" popularised by Java frameworks.) Inversion of control is sometimes referred to as the "Hollywood Principle: Don't call us, we'll call you". Inversion of control

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682-499: The more standard low-level details of providing a working system, thereby reducing overall development time. For example, a team using a web framework to develop a banking website can focus on writing code particular to banking rather than the mechanics of request handling and state management . Frameworks often add to the size of programs, a phenomenon termed " code bloat ". Due to customer-demand-driven applications needs, both competing and complementary frameworks sometimes end up in

713-417: The newer/evolved suite can be a product that shares integral utility libraries and user interfaces. This trend in the controversy brings up an important issue about frameworks. Creating a framework that is elegant, versus one that merely solves a problem, is still rather a craft than a science. "Software elegance " implies clarity, conciseness, and little waste (extra or extraneous functionality, much of which

744-407: The original meaning of granting the framework control flow (control over the time of execution of application code, e.g. callbacks). As an example, with traditional programming, the main function of an application might make function calls into a menu library to display a list of available commands and query the user to select one. The library thus would return the chosen option as the value of

775-474: The other case, it lies with the receiving application. The term was used by Michael Mattsson in a thesis (with its original meaning of a framework calling application code instead of vice versa) and was then taken from there by Stefano Mazzocchi and popularized by him in 1999 in a defunct Apache Software Foundation project, Avalon, in which it referred to a parent object passing in a child object's dependencies in addition to controlling execution flow. The phrase

806-434: The output product, nor its relative efficiency and conciseness. Using any library solution necessarily pulls in extras and unused extraneous assets unless the software is a compiler-object linker making a tight (small, wholly controlled, and specified) executable module. The issue continues, but a decade-plus of industry experience has shown that the most effective frameworks turn out to be those that evolve from re-factoring

837-476: The overall architecture of a software system, that is to say its basic components and the relationships between them. These remain unchanged (frozen) in any instantiation of the application framework. Hot spots represent those parts where the programmers using the framework add their own code to add the functionality specific to their own project. In an object-oriented environment, a framework consists of abstract and concrete classes . Instantiation of such

868-415: The program would be written using a software framework that knows common behavioral and graphical elements, such as windowing systems , menus, controlling the mouse, and so on. The custom code "fills in the blanks" for the framework, such as supplying a table of menu items and registering a code subroutine for each item, but it is the framework that monitors the user's actions and invokes the subroutine when

899-404: The project's staff; many programmers keep copies of useful boilerplate code for common needs. However, once a framework is learned, future projects can be faster and easier to complete; the concept of a framework is to make a one-size-fits-all solution set, and with familiarity, code production should logically rise. There are no such claims made about the size of the code eventually bundled with

930-546: The underlying technology on which they were built advanced. Even there, having evolved, many such packages will retain legacy capabilities bloating the final software as otherwise replaced methods have been retained in parallel with the newer methods. Software frameworks typically contain considerable housekeeping and utility code in order to help bootstrap user applications, but generally focus on specific problem domains, such as: According to Pree, software frameworks consist of frozen spots and hot spots . Frozen spots define

961-497: Was further popularized in 2004 by Robert C. Martin and Martin Fowler , the latter of whom traces the term's origins to the 1980s. In traditional programming, the flow of the business logic is determined by objects that are statically bound to one another. With inversion of control, the flow depends on the object graph that is built up during program execution. Such a dynamic flow is made possible by object interactions that are defined through abstractions. This run-time binding

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