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HELP VECTORCLASS                               John Williams, March 1986

      | Note: The more powerful construct -defclass- can now |
      | be used instead of -vectorclass-. See REF *DEFSTRUCT |

    vectorclass <classname> <fieldspec> ;
    vectorclass [identspec] <classname> [[:] <fieldspec>] ;

VECTORCLASS is a  macro that defines new vector  classes using *CONSKEY.
It  automatically  defines  constructor, destructor,  subscriptor,  fast
subscriptor, and recogniser procedures for the new class; and a variable
containing its key.

The <classname> specifies the dataword of the class.

The optional <fieldspec> specifies the type of elements of this class of
vectors. It should be either the  word "full" or an integer for integer-
only fields. If no <fieldspec> is  specified, the default is "full". See
REF *KEYS for more details.

The optional <identspec> specifies the status of the identifiers created
by VECTORCLASS.  One of "constant" and  "vars" may be used,  to indicate
that the  identifers should or should  not be made constant,  and one of
"procedure" or 0  may be used, to indicate their  *IDENTTYPE. If neither
"constant" nor "vars"  is specified, the identifier  status is defaulted
from the  variable *POPDEFINECONSTANT; if  neither "procedure" nor  0 is
specified,  the   identifier  type   is  defaulted  from   the  variable

-- Example -------------------------------------------------------------

The statement

    vectorclass short 16;

creates procedures

    initshort, consshort, destshort, isshort
    subscrshort, fast_subscrshort,

and declares the variable


with the new key as its value.

Vectors of type "short" can only contain integers in the range 0 to
(2 ** 16) - 1.

-- Recompiling a VECTORCLASS declaration ------------------------------

VECTORCLASS has been defined so that if you re-compile a file containing
a call of VECTORCLASS it will not construct a new key.  More precisely,
when a VECTORCLASS declaration is executed the value of the word
<name>_key is examined and if the value is a key and its specification
is the same as the specification in the declaration then a new key will
not be constructed, although the procedures associated with the key
(subscriptors, constructers etc.) will be reassigned to the variables
that should contain them.

This behaviour ensures that, if the declaration has not changed, then
the old subscriptor, recogniser, etc. will continue to work on
structures already created.  If for any reason you wish the declaration
to be re-executed, then you should assign soem non-key object (e.g.
undef) to the key name.  E.g. in the above example:

    undef -> short_key;

This will force the construction of a new key.  Any previously
constructed vectors will not work with the new subscriptor and will not
be recognised as instances of the new key.

-- See also ------------------------------------------------------------

    REF  *KEYS
    REF  *FILL

--- C.all/help/vectorclass
--- Copyright University of Sussex 1988. All rights reserved. ----------