The
format of a derived-type definition is:
TYPE [[, access-spec] ::] type-name |
[private-sequence-statement] ... |
component-definition-statement |
[component-definition-statement] ... |
- access-spec
is one of:
- type-name
is the name of the type being defined. type-name
must not conflict with the intrinsic type names.
- private-sequence-statement
is a PRIVATE
statement or a SEQUENCE
statement.
The use of PRIVATE
and PUBLIC is
only allowed if the type definition is within a module. Their use
is explained in Chapters 7 and 10.
The
SEQUENCE statement is explained below.
- component-definition-statement
is
type-spec [[component-attr-list]::] component-declaration |
- component-attr-list
can only contain the DIMENSION
and POINTER attributes.
- component-declaration
is
component-name [(component-array-spec)][*character-length] |
A component array without the POINTER
attribute must have an explicit-shape specification with constant
bounds.
The presence of the SEQUENCE
statement implies that the components of the type will be arranged
in storage in the order in which they are defined. The type is then
known as a sequence derived type. If
all components are of character type it has character sequence type,
and if all the components are of numeric type it has numeric sequence type.
Equivalencing
variables of derived type which have different sequence types is
a supported extension.
If a component is of the same derived type as the type being
defined then the component must have the POINTER
attribute.
For
example, a singly linked list can be created as a set of "nodes",
each containing a value and a pointer to the next node. A type node
can be defined as follows:
TYPE(node), POINTER :: next |
! next must have the POINTER |
Structure constructor |
 |
A structure constructor specifies
a scalar value for a derived type by specifying the values for the
components in the order that they appear in the definition. For
example:
CHARACTER(LEN=30) :: surname |
CHARACTER(LEN=20) :: firstname |
TYPE(employee) :: programmers(30) |
robjones=employee('Jones','Rob',20) |
programmers(1) = employee('Smith','John',34) |
employee('Smith','John',34)
is a structure constructor that contains the values assigned to
the components of the first element of the array programmers
by the final statement above.
Note that the name of the type must precede the parenthesized
data values of the components, a value must be present for each
component, and objects of derived type may be initialized by a structure
constructor in a derived-type declaration.
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