Type-Bound Procedures

In a derived-type definition, you can optionally specify a type-bound-procedure-part, which consists of a CONTAINS statement, optionally followed by a PRIVATE statement, and one or more procedure binding statements. Specific, GENERIC, and FINAL procedure bindings are defined below.

A type-bound-procedure-part in a derived-type definition declares one or more type-bound procedures. It takes the following form:

CONTAINS
[PRIVATE]
proc-binding-stmt
[ proc-binding-stmt]...

proc-binding-stmt

Is one of the following:

• specific-binding

• generic-binding

• final-binding

The default accessibility of type-bound procedures is public even if the components are private. You can change this by including the PRIVATE statement following the CONTAINS statement.

specific-binding
A specific type-bound procedure binds a procedure to a type or it specifies a deferred binding to an abstract type. It takes the following form:

PROCEDURE (interface-name), binding-attr-list :: binding-name [, binding-name]...

PROCEDURE [ [ , binding-attr-list ] :: ] binding-name [ => procedure-name ] [, [binding-name [ => procedure-name]]…]

interface-name

(Optional) Is the interface for the procedure. It must be the name of an abstract interface or a procedure that has an explicit interface. interface-name can only be specified if the binding has the DEFERRED attribute.

binding-attr-list

(Optional) Is one or more of the following. The same attribute can only appear once for the same binding:

• PASS [ (arg-name)]

  Defines the "passed-object dummy argument" of the procedure. If arg-name is specified, the interface of the binding must have a dummy argument named arg-name.

• NOPASS

  Indicates that the procedure has no passed-object dummy argument. Use this keyword if the procedure pointer component has an implicit interface or has no arguments. PASS and NOPASS can not both be specified for the same binding.

• access-spec

  Is the PUBLIC or PRIVATE attribute.

• NON_OVERRIDABLE

  Determines whether a binding can be overridden in an extended type. You must not specify NON_OVERRIDABLE for a binding with the DEFERRED attribute.

• DEFERRED

  Indicates that the procedure is deferred. Deferred bindings must only be specified for derived-type definitions with the ABSTRACT attribute. A procedure with the DEFERRED binding attribute must specify an interface-name. An overriding binding can have the DEFERRED attribute only if the binding it overrides is deferred. The NON_OVERRIDABLE and DEFERRED binding attributes must not both be specified for the same procedure.

binding-name

Is the name of the type-bound procedure. It is referred to in the same way as a component of a type.

procedure-name

(Optional) Is the name of the actual procedure which implements binding-name. It is the name of an accessible module procedure or an external procedure that has an explicit interface. It defines the interface for the procedure, and the procedure to be executed when the procedure is referenced.

If neither =>procedure-name nor interface-name appears, the procedure-name is the same as the binding-name. If =>procedure-name appears, you must specify the double-colon separator and you must not specify an interface-name.

In general, the invoking variable, the passed-object dummy argument, is passed as an additional argument. By default, this is the first dummy argument of the actual procedure. So, the first argument in the argument list becomes the second argument, etc.

A passed-object dummy argument can be changed by declaring the type-bound procedure with the PASS(arg-name) attribute. In this case, the variable is passed as the named argument. The PASS attribute can also be used to confirm the default as the first argument. The NOPASS attribute prevents passing the object as an argument.

Consider the following:

TYPE MY_TYPE
...   ! Component declarations
CONTAINS
  PROCEDURE :: PROC1 => MY_PROC
  PROCEDURE :: PROC2, PROC3 => MY_PROC3
  PROCEDURE :: PROC4 => MY_PROC4, PROC5 => MY_PROC5
END TYPE MY_TYPE

This binds MY_PROC with the PROC1.

If B is a scalar variable of type MY_TYPE, an example of a type-bound call is:

CALL B%PROC1(C, D)

When PASS is in effect, the call passes B to the first argument of the procedure, C to the second argument, and D to the third argument.

generic-binding
A generic type-bound procedure defines a generic interface that is bound to the type. For more information, see the GENERIC statement.

final-binding
An extensible derived type can have one or more "final subroutines" associated with it. A final subroutine can be executed to perform clean-up operations after a data entity of that type is finalized (ceases to exist). For more information, see the FINAL statement.