The C++ Standard Library provides many different function object adaptors, including (that returns the logical complement of the value returned by a particular adaptable predicate), and and , which perform composition of function object.
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It is conceptually similar to the expression: (setf (fdefinition 'f) #'(lambda (a) (block f b...))) where is a macro used to set the value of the first argument to a new function object. is a global function definition for the function named . is an abbreviation for special operator, returning a function object.
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In languages such as Lua, more sophisticated techniques exist which allow a function to be replaced by a new function with the same name, which would permit: factorial = construct-memoized- functor(factorial) Essentially, such techniques involve attaching the original function object to the created functor and forwarding calls to the original function being memoized via an alias when a call to the actual function is required (to avoid endless recursion), as illustrated below: function construct-memoized-functor (F is a function object parameter) allocate a function object called memoized-version; let memoized-version(arguments) be if self has no attached array values then [self is a reference to this object] allocate an associative array called values; attach values to self; allocate a new function object called alias; attach alias to self; [for later ability to invoke F indirectly] self.alias = F; end if; if self.values[arguments] is empty then self.values[arguments] = self.
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Finally, the entry in the array at the key position is returned to the caller. The above strategy requires explicit wrapping at each call to a function that is to be memoized. In those languages that allow closures, memoization can be effected implicitly by a functor factory that returns a wrapped memoized function object. In pseudocode, this can be expressed as follows: function construct-memoized-functor (F is a function object parameter) allocate a function object called memoized-version; let memoized-version(arguments) be if self has no attached array values then [self is a reference to this object] allocate an associative array called values; attach values to self; end if; if self.
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In general, a function object has restrictions on the type of its argument. The type restrictions need not be simple, though: may be overloaded or may be a member template. Similarly, there need be no way for a program to determine what those restrictions are. An adaptable function object, however, does specify what the argument and return types are, and provides nested s so that those types can be named and used in programs.
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WITH-OPEN-FILE is a macro that opens a file and provides a stream. When the form is returning, the file is automatically closed. FUNCALL calls a function object. The LOOP collects all lines that match the predicate.
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Functors are very useful in modeling functional effects to apply a function to computations that did not yet finish. Functors form a base for more complex abstractions like Applicative, Monad, Comonad. In C++, the name functor refers to a function object instead of this definition.
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In computer programming, a function object is a construct allowing an object to be invoked or called as if it were an ordinary function, usually with the same syntax (a function parameter that can also be a function). Function objects are often called functors.
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In the context of the programming language C++, `functional` refers to a header file that is part of the C++ Standard Library and provides a set of predefined class templates for function objects, including operations for arithmetic, comparisons, and logic. Instances of these class templates are C++ classes that define a function call operator, and the instances of these classes can be called as if they were functions. It is possible to perform very sophisticated operations without writing a new function object, simply by combining predefined function objects and function object adaptors. The class template `std::function` provided by C++11 is a general-purpose polymorphic function wrapper.
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A typical use of a function object is in writing callback functions. A callback in procedural languages, such as C, may be performed by using function pointers. However it can be difficult or awkward to pass a state into or out of the callback function. This restriction also inhibits more dynamic behavior of the function.
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Functions are objects themselves, which can be used to produce an effect similar to "static properties" (using C++/Java terminology) as shown below. (The function object also has a special `prototype` property, as discussed in the "Inheritance" section below.) Object deletion is rarely used as the scripting engine will garbage collect objects that are no longer being referenced.
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It is created each time the outer function is invoked. In addition, each nested function forms a lexical closure: The lexical scope of the outer function (including any constant, local variable, or argument value) becomes part of the internal state of each inner function object, even after execution of the outer function concludes. JavaScript also supports anonymous functions.
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A function object solves those problems since the function is really a façade for a full object, carrying its own state. Many modern (and some older) languages, e.g. C++, Eiffel, Groovy, Lisp, Smalltalk, Perl, PHP, Python, Ruby, Scala, and many others, support first-class function objects and may even make significant use of them. Functional programming languages additionally support closures, i.e.
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These four modules are added to the `` header file: Polymorphic function wrapper (`function`) – can store any callable function (function pointers, member function pointers, and function objects) that uses a specified function call signature. The type does not depend on the kind of the callable used. Based on Boost.Function Function object binders (`bind`) – can bind any parameter parameters to function objects.
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The more risk the usage of the function/object has, the more thorough the testing that is needed. The same can be said for complexity. Risk and complexity analysis determines the test design techniques to be applied for a given specification. Historical data of your previous developments help setting the best set of test design techniques to reach a cost optimum and high quality together.
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An object can be initialized by any one of the following ways. a. Through declaration Object b = a; // translates as Object::Object(const Object&) (invoke copy constructor) b. Through function arguments type function(Object a); c. Through function return value Object a = function(); The copy constructor is used only for initializations, and does not apply to assignments where the assignment operator is used instead.
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C++ enables defining function objects by overloading `operator()`. These objects behave somewhat like functions in a functional programming language. They may be created at runtime and may contain state, but they do not implicitly capture local variables as closures do. As of the 2011 revision, the C++ language also supports closures, which are a type of function object constructed automatically from a special language construct called lambda- expression.
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The function that does this value-for-function-object replacement can generically wrap any referentially transparent function. Consider the following pseudocode (where it is assumed that functions are first-class values): function memoized-call (F is a function object parameter) if F has no attached array values then allocate an associative array called values; attach values to F; end if; if F.values[arguments] is empty then F.values[arguments] = F(arguments); end if; return F.values[arguments]; end function In order to call an automatically memoized version of `factorial` using the above strategy, rather than calling `factorial` directly, code invokes `memoized- call(factorial(n))`. Each such call first checks to see if a holder array has been allocated to store results, and if not, attaches that array. If no entry exists at the position `values[arguments]` (where `arguments` are used as the key of the associative array), a real call is made to `factorial` with the supplied arguments.
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If a type is a model of an adaptable generator, then it must define . Similarly, if is a model of the adaptable unary function, it must define and , and if is a model of the adaptable binary function, it must define , , and . The C++ Standard Library provides base classes and to simplify the definition of adaptable unary functions and adaptable binary functions. Adaptable function objects are important, because they can be used by function object adaptors: function objects that transform or manipulate other function objects.
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AngularJS uses the term "scope" in a manner akin to the fundamentals of computer science. Scope in computer science describes when in the program a particular binding is valid. The ECMA-262 specification defines scope as: a lexical environment in which a Function object is executed in client-side web scripts; akin to how scope is defined in lambda calculus. As a part of the "MVC" architecture, the scope forms the "Model", and all variables defined in the scope can be accessed by the "View" as well as the "Controller".
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C++ provides support for anonymous functions, also known as lambda expressions, with the following form: [capture](parameters) -> return_type { function_body } If the lambda takes no parameters, the () can be omitted, that is, [capture] -> return_type { function_body } Also, the return type of a lambda expression can be automatically inferred, if possible, e.g.: [](int x, int y) { return x + y; } // inferred [](int x, int y) -> int { return x + y; } // explicit The [capture] list supports the definition of closures. Such lambda expressions are defined in the standard as syntactic sugar for an unnamed function object.
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The basic idea is to objectify (encapsulate as an object) a function independent of any other enclosing concept (e.g. decoupling an object function from any direct knowledge of the enclosing object). See First-class function for further insight into functions as objects, which qualifies as one form of first-class function. So, for example, in an object-oriented language, when a function of an object is referenced as an object (freeing it from having any knowledge of its enclosing host object) the new function object can be passed, stored, and called at a later time.
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While the C++03 language provides a memory model that supports threading, the primary support for actually using threading comes with the C++11 standard library. A thread class (`std::thread`) is provided, which takes a function object (and an optional series of arguments to pass to it) to run in the new thread. It is possible to cause a thread to halt until another executing thread completes, providing thread joining support via the `std::thread::join()` member function. Access is provided, where feasible, to the underlying native thread object(s) for platform-specific operations by the `std::thread::native_handle()` member function.
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A priority queue is often considered to be a "container data structure". The Standard Template Library (STL), and the C++ 1998 standard, specifies `priority_queue` as one of the STL container adaptor class templates. However, it does not specify how two elements with same priority should be served, and indeed, common implementations will not return them according to their order in the queue. It implements a max-priority-queue, and has three parameters: a comparison object for sorting such as a function object (defaults to less if unspecified), the underlying container for storing the data structures (defaults to std::vector), and two iterators to the beginning and end of a sequence.
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In class-based programming, a factory is an abstraction of a constructor of a class, while in prototype- based programming a factory is an abstraction of a prototype object. A constructor is concrete in that it creates objects as instances of a single class, and by a specified process (class instantiation), while a factory can create objects by instantiating various classes, or by using other allocation schemes such as an object pool. A prototype object is concrete in that it is used to create objects by being cloned, while a factory can create objects by cloning various prototypes, or by other allocation schemes. Factories may be invoked in various ways, most often a method call (a factory method), sometimes by being called as a function if the factory is a function object (a factory function).
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