Top 90: Defined Type: Definition 
Copyright (c) 1994 J. Adams, W. Brainerd, J. Martin, and B. Smith.
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20 Defined Type: Definition

User-defined data types, officially called derived types, are built of components of intrinsic or user-defined type; ultimately, the components are of intrinsic type. This permits the creation of objects, called structures, that contain components of different types (unlike arrays, which are homogeneous). It also permits objects, both scalars and arrays, to be declared to be of a user-defined type and operations to be defined on such objects. A component may be a pointer, which provides for dynamic data structures, such as lists and trees. Defined types provide the basis for building abstract data types.

Examples:

TYPE TEMP_RANGE                ! This is a simple example of
   INTEGER HIGH, LOW           !    a defined type with two
END TYPE TEMP_RANGE            !    components, HIGH and LOW.

TYPE TEMP_RECORD               ! This type uses the previous
   CHARACTER(LEN=40) CITY      !    definition for one component.
   TYPE (TEMP_RANGE) EXTREMES(1950:2050)
END TYPE TEMP_RECORD

TYPE LINKED_LIST               ! This one has a pointer compon-
   REAL VALUE                  !    ent to provide links to other
   TYPE(LINKED_LIST),POINTER :: NEXT !  objects of the same type,
END TYPE LINKED_LIST           !    thus providing linked lists.

TYPE, PUBLIC :: SET; PRIVATE        ! This is a public type whose
   INTEGER CARDINALITY              !   component structure is
   INTEGER ELEMENT ( MAX_SET_SIZE ) !   private; defined
END TYPE SET                        !   operations provide
                                    !   all functionality.

! Declare scalar and array structures of type SET.
TYPE (SET) :: BAKER, FOX(1:SIZE(HH))

Related Topics:

Defined Type: Operators and Assignment
Defined Type: Objects and Statements
Defined Type: Structure Component
Defined Type: Structure Constructor
Generic Procedures and Operators
Interfaces and Interface Blocks
Modules
PUBLIC and PRIVATE Attributes
Scope, Association, and Definition Overview
USE Statement and Use Association

To Read More About It:

ISO 1539 : 1991, Fortran Standard, 4.4, 11.3.3.3, C.11.4
Fortran 90 Handbook, 4.4, 11.6.5.3-5
Programmer's Guide to Fortran 90, 6, 7

A defined-type definition is:

TYPE [ [ , access-spec ] :: ] type-name
[ PRIVATE ]
[ SEQUENCE ]
component-declaration
[ component-declaration ]...
END TYPE [ type-name ]

A component declaration is:

type-spec [ [ , component-attribute-list ] :: ] component-list

A component attribute is one of:

POINTER
DIMENSION ( array-spec )

Things To Know:

  1. A type name may be any legal Fortran 90 name as long as it is not the same as an intrinsic type name or another local name (except component names and actual argument keyword names) in that scoping unit. A type definition forms its own scoping unit, which means that the component names are not restricted by the occurrence of any names outside the type definition; the scoping unit has access to host objects by host association so that constants may be used in component declaration.
  2. A component array specification must be explicit shape or deferred shape; a deferred shape component must have the POINTER attribute.
  3. A component may itself be a defined type. If, in addition, the POINTER attribute is specified, the component type may even be that of the type being defined; this is the only instance in which recursion is permitted in a defined-type definition.
  4. A defined type may contain an access specification (PUBLIC or PRIVATE attribute) or an internal PRIVATE statement only if it is in a module.
  5. The internal PRIVATE statement in a type definition makes the components unavailable outside the module even though the type itself might be available.
  6. The SEQUENCE statement is used if: (1) objects of this type are to be storage associated, or (2) ``equivalent'' type definitions are to be used with actual and dummy arguments.
  7. Operations on defined types are defined with procedures and given