Interface concepts
- The characteristics of the procedure
- The name of the procedure
- The name and characteristics of each dummy argument
- The generic identifiers of the procedure, if any
- Distinguishing the procedure as a subroutine or a function
- Distinguishing each dummy argument either as a data object, dummy
procedure, or alternate return specifier
The characteristics of a dummy data object are its declared type, type parameters (if any), shape
(unless it is assumed-rank)
, intent, whether
it is optional, allocatable, 
polymorphic, 
a pointer,
a target, or has the VALUE or 
CONTIGUOUS
attribute. Any dependence on other objects for type
parameter or array bound determination is a characteristic. If a shape,
size, or character length is assumed or deferred, it is a characteristic.The characteristics of a dummy procedure are the explicitness of its interface, its procedure characteristics (if the interface is explicit), and whether it is optional.
- If the procedure is a function, it specifies the characteristics
of the result value, specifically:
- Declared type
- Any type parameters
- Rank
- Whether the result value is a pointer
- Whether the result value is a procedure pointer
- Whether the result value is allocatable.
- Whether
the result value is polymorphic
- Whether the result value is contiguous.
- Determine whether the procedure is PURE or ELEMENTAL.
- Determine
if the procedure has the BIND attribute.
If a procedure is accessible in a scoping unit, it has an interface that is either explicit or implicit in that scoping unit. The rules are:
| Entity | Interface |
|---|---|
| Dummy procedure | Explicit in a scoping unit if an interface block exists or is accessible, or if an explicit interface is specified by a PROCEDURE declaration statement. Implicit in all other cases. |
| External subprogram | Explicit in a scoping unit other than its own if an interface block exists or is accessible, or if an explicit interface is specified by a PROCEDURE declaration statement. Implicit in all other cases. |
| Recursive procedure with a result clause | Explicit in the subprogram's own scoping unit. |
| Module procedure | Always explicit. |
| Internal procedure | Always explicit. |
| Generic procedure | Always explicit. |
| Intrinsic procedure | Always explicit. |
| Statement function | Always implicit. |
Internal subprograms cannot appear in an interface block or in a PROCEDURE declaration statement.
A procedure must not have more than one accessible interface in a scoping unit.
The interface of a statement function cannot be specified in an interface block or in a PROCEDURE declaration statement.
