Generic programming
Generic programming is a programming paradigm that deals with sets of language entities rather with individual instances of. The sets can consist of:
- subprograms (generic function);
- types and classes of (generic types);
- objects (generic object);
- compilation units (generic package).
For example, a generic function describes a set of functions, etc.
Such generic sets are called generics or templates. Being a set, the generics itself is not yet a subject of the programming language. It must first be constrained to an element of in order to identify a concrete subprogram, type, object, package, etc. So the language of generics constitutes a meta language relatively to the underlying programming language (the object language).
The process of constraining of a generics is called instantiation. The result of is a generic instance. Instantiation can be
Instantiation constraints the generic set by defining generic formal parameters. What can serve as a generic formal parameter depends on the language. In the most general case it can be a subprogram, type, object, instance of another generics.
Partial definition or constraining of some of generic formal parameters of a generics is called generic specialization. Specialization produces another generic rather than an instance of.
As any other programming language, the meta language of generics can be typed. In a typed language of generics, substitution of an actual generic parameter is checked upon instantiation against the formal generic type. The choice does not necessarily depend on the object language. For example, C++ is typed, but its language of generics is not.
Generics are sometimes said to be parametric or else static polymorphism. The effect of generic programming in object-oriented programming is achieved by means dynamic polymorphism. In this case generic programming is narrowed to the programming in terms of sets of types (i.e. classes), rather than arbitrary sets of language entities.
Historically generic programming first appeared in the form of macro languages and preprocessors.