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Declaration: Definitions vs Declarations, Definitions and Declarations (computer programming): Type declaration - User-defined type declaration, Variable declaration - Constant declaration, Class declaration - Object declaration, Constructor declaration - Destructor declaration, Struct declaration - Record declaration, Function declaration - Method declaration, Lambda declaration - Anonymous function declaration, Enumerator declaration, Pointer declaration, Generic declaration - Template declaration, Interface declaration - Protocol declaration - Trait declaration, Namespace declaration, Package declaration, Module declaration, Alias declaration, Import declaration - Export declaration, Macro declaration. Programming terms. (navbar_declaration)
Templates are a feature of the C++ programming language that allows functions and classes to operate with generic types. This allows a function or class declaration to reference via a generic variable another different class (built-in or newly declared data type) without creating full declaration for each of these different classes.
In plain terms, a templated class or function would be the equivalent of (before "compiling") copying and pasting the templated block of code where it is used, and then replacing the template parameter with the actual one. For this reason, classes employing templated methods place the implementation in the headers (*.h files) as no symbol could be compiled without knowing the type beforehand.
The C++ Standard Library provides many useful functions within a framework of connected templates.
Major inspirations for C++ templates were the parameterized modules provided by the language CLU and the generics provided by Ada.
In computer programming, a declaration is a language construct specifying identifier properties: it declares a word's (identifier's) meaning. Declarations are most commonly used for functions, variables, constants, and classes, but can also be used for other entities such as enumerations and type definitions. Beyond the name (the identifier itself) and the kind of entity (function, variable, etc.), declarations typically specify the data type (for variables and constants), or the type signature (for functions); types may also include dimensions, such as for arrays. A declaration is used to announce the existence of the entity to the compiler; this is important in those strongly typed languages that require functions, variables, and constants, and their types to be specified with a declaration before use, and is used in forward declaration. The term "declaration" is frequently contrasted with the term "definition", but meaning and usage varies significantly between languages; see below.
Declarations are particularly prominent in languages in the ALGOL tradition, including the BCPL family, most prominently C and C++, and also Pascal. Java uses the term "declaration", though Java does not require separate declarations and definitions.
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