HP Fortran Programmer's Reference

HP Fortran statements
OPTIONAL (statement and attribute)
OPTIONAL (statement and attribute)
Identifies optional arguments for procedures.
Syntax
The syntax of the type declaration statement with the OPTIONAL attribute is:
type , attrib-list :: dummy-argument-name-list
type
attrib-list
Table 10-41
dummy-argument-name-list
382
is a valid type specification (INTEGER, REAL, LOGICAL, CHARACTER, TYPE (
name), etc.).
is a comma-separated list of attributes including OPTIONAL and optionally
those attributes compatible with it, namely:
DIMENSION INTENT TARGET
EXTERNAL POINTER VOLATILE
is a comma-separated list of dummy-argument-names.
The syntax of the OPTIONAL statement is:
OPTIONAL [::] dummy-argument-name-list
Description
If a dummy argument has the OPTIONAL attribute, the corresponding actual argument need
not appear in a procedure reference. In cases where there are arguments that generally do not
change from one reference to another, it is convenient to specify that the arguments are
optional and provide default values for them. They can then be omitted from references in
these general cases. The presence of an optional argument in a procedure may be determined
by using the PRESENT intrinsic function.
Many uses of the ENTRY statement in FORTRAN 77 programs can be replaced by the use of
optional arguments.
ThefollowingrestrictionsapplytotheuseoftheOPTIONAL attribute:
Chapter 10