In
computer programming, a
declaration specifies properties of an
identifier: it declares what a word (identifier)
means. 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.