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In computer programming, a callback is a function that is stored as data (a reference) and designed to be called by another function – often back to the original abstraction layer. A function that accepts a callback parameter may be designed to call back before returning to its caller which is known as synchronous or blocking .
The debugging interface of Eclipse with a program suspended at a breakpoint. Panels with stack trace (upper left) and watched variables (upper right) can be seen. In software development, a breakpoint is an intentional stopping or pausing place in a program, put in place for debugging purposes. It is also sometimes simply referred to as a pause
Notice that the syntax for providing the callback to the std::sort() function is identical, but an object is passed instead of a function pointer. When invoked, the callback function is executed just as any other member function, and therefore has full access to the other members (data or functions) of the object.
In an event-driven application, there is generally an event loop that listens for events and then triggers a callback function when one of those events is detected. Event-driven programs can be written in any programming language , although the task is easier in languages that provide high-level abstractions .
The assignment statement (=) binds a name as a reference to a separate, dynamically allocated object. Variables may subsequently be rebound at any time to any object. In Python, a variable name is a generic reference holder without a fixed data type; however, it always refers to some object with a type.
This is followed by the function name, formal arguments in parentheses, and body lines in braces. In C++, a function declared in a class (as non-static) is called a member function or method. A function outside of a class can be called a free function to distinguish it from a member function. [29]
The term closure is often used as a synonym for anonymous function, though strictly, an anonymous function is a function literal without a name, while a closure is an instance of a function, a value, whose non-local variables have been bound either to values or to storage locations (depending on the language; see the lexical environment section below).
One can also pass a callback method to BeginAccomplish, to be invoked when the long-running method completes. It typically calls EndAccomplish to obtain the return value of the long-running method. A problem with the callback mechanism is that the callback function is naturally executed in the worker thread (rather than in the original calling ...