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Static Semantics

A type is characterized by a set of values, and a set of primitive
operations which implement the fundamental aspects of its semantics. An
object of a given type is a runtime entity that contains (has) a value
of the type.

Types are grouped into classes of types, reflecting the similarity of
their values and primitive operations. There exist several
languagedefined classes of types (see NOTES below). Elementary types
are those whose values are logically indivisible; composite types are
those whose values are composed of component values.

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

The composite types are the record types, record extensions, array
types, task types, and protected types. A private type or private
extension represents a partial view, See section 7.3 Private Types and Private Extensions, of a type, providing
support for data abstraction. A partial view is a composite type.

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.

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. Similarly, a part of an object or value is
used to mean the whole object or value, or any set of its subcomponents.

The set of possible values for an object of a given type can be
subjected to a condition that is called a 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
See section 3.5 Scalar Types for range_constraints, See section 3.6.1 Index Constraints and Discrete Ranges, for index_constraints,
and See section 3.7.1 Discriminant Constraints, for discriminant_constraints.

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. Such values belong to the 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).
NOTES

(2) Any set of types that is closed under derivation See section 3.4 Derived Types and Classes, 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 section 3.2.3 Classification of Operations, or
that correspond to a set of types that are matched by a given kind of
generic formal type See section 12.5 Formal Types. The following are examples of
"interesting" languagedefined classes: elementary, scalar, discrete,
enumeration, character, boolean, integer, signed integer, modular, real,
floating point, fixed point, ordinary fixed point, decimal fixed point,
numeric, access, accesstoobject, accesstosubprogram, composite,
array, string, (untagged) record, tagged, task, protected, nonlimited.
Special syntax is provided to define types in each of these classes.

These languagedefined classes are organized like this:

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
accesstoobject
accesstosubprogram
composite
array
string
other array
untagged record
tagged
task
protected

The classes "numeric" and "nonlimited" represent other
classification dimensions and do not fit into the above strictly
hierarchical picture.
 3.2.1: Type Declarations
 3.2.2: Subtype Declarations
 3.2.3: Classification of Operations
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