1

{*type*} {*primitive
operation* [partial]} A *type* is
characterized by a set of values, and a set of *primitive operations*
which implement the fundamental aspects of its semantics. {*object*
[partial]} An *object* of a given type
is a run-time entity that contains (has) a value of the type.

1.a

1.b

2

{*class (of types)*}
Types are grouped into *classes* of types, reflecting
the similarity of their values and primitive operations. {*language-defined
class (of types)*} There exist several
*language-defined classes* of types (see NOTES below). {*elementary
type*} *Elementary* types are those
whose values are logically indivisible; {*composite type*}
{*component*} *composite*
types are those whose values are composed of *component* values.
{*aggregate: See also composite type*}

2.a

2.b

2.c

2.d

2.e

2.f

2.g

2.h

2.i

2.j

2.k

2.l

2.m

2.n

2.o

2.p

2.q

3

{*scalar type*} The
elementary types are the *scalar* types (*discrete* and *real*)
and the *access* types (whose values provide access to objects or
subprograms). {*discrete type*} {*enumeration
type*} Discrete types are either *integer*
types or are defined by enumeration of their values (*enumeration*
types). {*real type*} Real
types are either *floating point* types or *fixed point* types.

4

The composite types are the *record* types,
*record extensions*, *array* types, *task* types, and
*protected* types. {*private type*} {*private
extension*} A *private* type or *private
extension* represents a partial view (see 7.3)
of a type, providing support for data abstraction. A partial view is
a composite type.

4.a

5

{*discriminant*} Certain
composite types (and partial views thereof) have special components called
*discriminants* whose values affect the presence, constraints, or
initialization of other components. Discriminants can be thought of as
parameters of the type.

6

{*subcomponent*} The
term *subcomponent* is used in this International Standard in place
of the term component to indicate either a component, or a component
of another subcomponent. Where other subcomponents are excluded, the
term component is used instead. {*part (of an object
or value)*} Similarly, a *part* of
an object or value is used to mean the whole object or value, or any
set of its subcomponents.

6.a

6.b

We use the term ``part'' when
talking about the parent part, ancestor part, or extension part of a
type extension. In contexts such as these, the part might represent an
empty set of subcomponents (e.g. in a null record extension, or a nonnull
extension of a null record). We also use ``part'' when specifying rules
such as those that apply to an object with a ``controlled part'' meaning
that it applies if the object as a whole is controlled, or any subcomponent
is.

7

{*constraint* [partial]}
The set of possible values for an object of a given
type can be subjected to a condition that is called a *constraint*
{*null constraint*} (the
case of a *null constraint* that specifies no restriction is also
included)[; the rules for which values satisfy a given kind of constraint
are given in 3.5 for range_constraints,
3.6.1 for index_constraints,
and 3.7.1 for discriminant_constraints].

8

{*subtype*} A
*subtype* of a given type is a combination of the type, a constraint
on values of the type, and certain attributes specific to the subtype.
The given type is called the type *of* the subtype. Similarly, the
associated constraint is called the constraint *of* the subtype.
The set of values of a subtype consists of the values of its type that
satisfy its constraint. {*belong (to a subtype)*}
Such values *belong* to the subtype.

8.a

8.b

8.c

8.d

8.e

9

{*constrained*} {*unconstrained*}
{*constrained (subtype)*}
{*unconstrained (subtype)*}
A subtype is called an *unconstrained* subtype
if its type has unknown discriminants, or if its type allows range, index,
or discriminant constraints, but the subtype does not impose such a constraint;
otherwise, the subtype is called a *constrained* subtype (since
it has no unconstrained characteristics).

9.a

9.b

For scalar types, ``constrained''
means ``has a non-null constraint''. For composite types, in implementation
terms, ``constrained'' means that the size of all objects of the subtype
is the same, assuming a typical implementation model.

9.c

Class-wide subtypes are always
unconstrained.

NOTES

10

2 Any set of types that is
closed under derivation (see 3.4) can be called
a ``class'' of types. However, only certain classes are used in the description
of the rules of the language -- generally those that have their own particular
set of primitive operations (see 3.2.3),
or that correspond to a set of types that are matched by a given kind
of generic formal type (see 12.5). {*language-defined
class* [partial]} The following are examples
of ``interesting'' *language-defined classes*: elementary, scalar,
discrete, enumeration, character, boolean, integer, signed integer, modular,
real, floating point, fixed point, ordinary fixed point, decimal fixed
point, numeric, access, access-to-object, access-to-subprogram, composite,
array, string, (untagged) record, tagged, task, protected, nonlimited.
Special syntax is provided to define types in each of these classes.

10.a

10.b

10.c

Not every property of types represents
a class. For example, the set of all abstract types does not form a class,
because this set is not closed under derivation.

10.d

The set of limited types forms
a class in the sense that it is closed under derivation, but the more
interesting class, from the point of generic formal type matching, is
the set of all types, limited and nonlimited, since that is what matches
a generic formal ``limited'' private type. Note also that a limited type
can ``become nonlimited'' under certain circumstances, which makes ``limited''
somewhat problematic as a class of types.

11

These language-defined classes are organized
like this:

12

all types

elementary

scalar

discrete

enumeration

character

boolean

other enumeration

integer

signed integer

modular integer

real

floating point

fixed point

ordinary fixed point

decimal fixed point

access

access-to-object

access-to-subprogram

composite

array

string

other array

untagged record

tagged

task

protected

elementary

scalar

discrete

enumeration

character

boolean

other enumeration

integer

signed integer

modular integer

real

floating point

fixed point

ordinary fixed point

decimal fixed point

access

access-to-object

access-to-subprogram

composite

array

string

other array

untagged record

tagged

task

protected

13

The classes ``numeric'' and ``nonlimited''
represent other classification dimensions and do not fit into the above
strictly hierarchical picture.

13.a

This clause and its subclauses
now precede the clause and subclauses on objects and named numbers, to
cut down on the number of forward references.

13.b

We have dropped the term "base
type" in favor of simply "type" (all types in Ada 83 were
"base types" so it wasn't clear when it was appropriate/necessary
to say "base type"). Given a subtype S of a type T, we call
T the "type of the subtype S."