First-class Object

In Computing , a first-class object (also '''-value''', '''-entity''', '''-citizen'''), in the context of a particular Programming Language , is an entity which can be used in programs without restriction (when compared to other kinds of objects in the same language). Depending on the language, this can imply:

being expressible as an anonymous Literal Value

being storable in Variables

being storable in Data Structures

having an intrinsic identity (independent of any given name)

being comparable for equality with other entities

being passable as a parameter to a procedure/function

being returnable as the result of a procedure/function

being constructable at Runtime

For example, in C , it is not possible to create new Function s at runtime, whereas other kinds of object can be created at runtime. So functions in C are not first-class objects; sometimes they are called second-class objects because they can still be manipulated in most of the above fashions (via Function Pointer s). Similarly, String s are not first class objects in Fortran as it is not possible to assign them to variables, whereas numbers can be so assigned.

SEE ALSO

First Class Function

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First-class Object

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