nil

#nil

##Syntax nil [ (collectionOrClassId ) ]

##Description The nil pointer does not locate any element (object). Pointers locate items in collections, classes and types. The collectionOrClassId is optional.

This nil pointer is distinct from pointers to actual elements, and it can be compared to these pointers. It is also distinct from the uninitialized pointer value.

##Example In this example, the pointer called first is set to the nil pointer of collection c, that is, to nil(c).

    var c : collection of
        record
            name : string ( 50 )
            next : pointer to c
        end record
    var first : pointer to c := nil ( c )

##Details See also collection, class and pointer. When nil is written without the collectionOrClassId, it can be assigned to a pointer to any collection, class or type.

The type of nil without the collectionOrClassId is effectively a pointer to everyClass, an imaginary class that has no objects and is the descendant of all classes. This implies that it can be assigned to any other class pointer, because it is a descendant of all classes.

Turing allows you to write nil (id) after a forward declaration of id (the name of a collection, class or type) before (and after) the resolution of the id.