Pure Virtual Class
In programming languages, an abstract type (also known as existential types) is a Type (computer science), type in a nominative type system that cannot be Instance (computer science), instantiated directly; by contrast, a concrete type be instantiated directly. Instantiation of an abstract type can occur only indirectly, via a concrete Subtyping, ''subtype''. An abstract type may provide no implementation, or an incomplete implementation. In some languages, abstract types with no implementation (rather than an incomplete implementation) are known as ''Protocol (object-oriented programming), protocols'', ''interfaces'', ''signatures'', or ''class types''. In Class-based programming, class-based object-oriented programming, abstract types are implemented as ''abstract class, abstract classes'' (also known as ''abstract base classes''), and concrete types as ''concrete classes''. In generic programming, the analogous notion is a Concept (generic programming), ''concept'', which s ...
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Programming Languages
A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their syntax (form) and semantics (meaning), usually defined by a formal language. Languages usually provide features such as a type system, variables, and mechanisms for error handling. An implementation of a programming language is required in order to execute programs, namely an interpreter or a compiler. An interpreter directly executes the source code, while a compiler produces an executable program. Computer architecture has strongly influenced the design of programming languages, with the most common type ( imperative languages—which implement operations in a specified order) developed to perform well on the popular von Neumann architecture. While early programming languages were closely tied to the hardware, over time they have developed more abstraction to hide implementation details for greater simplicity. Thousands of programming langua ...
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