- This Annex contains informal descriptions of some terms used in this
International Standard. To find more formal definitions, look the term up in
- Access type. An access type has values that designate aliased objects.
Access types correspond to ``pointer types'' or ``reference types'' in some
- Aliased. An aliased view of an object is one that can be designated by
an access value. Objects allocated by allocators are aliased. Objects can
also be explicitly declared as aliased with the reserved word aliased. The
Access attribute can be used to create an access value designating an aliased
- Array type. An array type is a composite type whose components are all
of the same type. Components are selected by indexing.
- Character type. A character type is an enumeration type whose values
- Class. A class is a set of types that is closed under derivation,
which means that if a given type is in the class, then all types derived from
that type are also in the class. The set of types of a class share common
properties, such as their primitive operations.
- Compilation unit. The text of a program can be submitted to the compiler
in one or more compilations. Each compilation is a succession of
compilation_units. A compilation_unit contains either the declaration, the
body, or a renaming of a program unit.
- Composite type. A composite type has components.
- Construct. A construct is a piece of text (explicit or implicit) that is
an instance of a syntactic category defined under ``Syntax.''
- Controlled type. A controlled type supports user-defined assignment and
finalization. Objects are always finalized before being destroyed.
- Declaration. A declaration is a language construct that associates a
name with (a view of) an entity. A declaration may appear explicitly in the
program text (an explicit declaration), or may be supposed to occur at a
given place in the text as a consequence of the semantics of another
construct (an implicit declaration).
- Definition. All declarations contain a definition for a view of an
entity. A view consists of an identification of the entity (the entity of
the view), plus view-specific characteristics that affect the use of the
entity through that view (such as mode of access to an object, formal
parameter names and defaults for a subprogram, or visibility to components of
a type). In most cases, a declaration also contains the definition for the
entity itself (a renaming_declaration is an example of a declaration that
does not define a new entity, but instead defines a view of an existing
entity (see 8.5)).
- Derived type. A derived type is a type defined in terms of another
type, which is the parent type of the derived type. Each class containing
the parent type also contains the derived type. The derived type inherits
properties such as components and primitive operations from the parent. A
type together with the types derived from it (directly or indirectly) form a
- Discrete type. A discrete type is either an integer type or an
enumeration type. Discrete types may be used, for example, in case_statements and as array indices.
- Discriminant. A discriminant is a parameter of a composite type. It
can control, for example, the bounds of a component of the type if that type
is an array type. A discriminant of a task type can be used to pass data to
a task of the type upon creation.
- Elementary type. An elementary type does not have components.
- Enumeration type. An enumeration type is defined by an enumeration of
its values, which may be named by identifiers or character literals.
- Exception. An exception represents a kind of exceptional situation; an
occurrence of such a situation (at run time) is called an exception
occurrence. To raise an exception is to abandon normal program execution
so as to draw attention to the fact that the corresponding situation has
arisen. Performing some actions in response to the arising of an exception
is called handling the exception.
- Execution. The process by which a construct achieves its run-time
effect is called execution. Execution of a declaration is also called
elaboration. Execution of an expression is also called evaluation.
- Generic unit. A generic unit is a template for a (nongeneric) program
unit; the template can be parameterized by objects, types, subprograms, and
packages. An instance of a generic unit is created by a generic_instantiation. The rules of the language are enforced when a generic unit is
compiled, using a generic contract model; additional checks are performed
upon instantiation to verify the contract is met. That is, the declaration
of a generic unit represents a contract between the body of the generic and
instances of the generic. Generic units can be used to perform the role that
macros sometimed play in other languages.
- Integer type. Integer types comprise the signed integer types and the
modular types. A signed integer type has a base range that includes both
positive and negative numbers, and has operations that may raise an exception
when the result is outside the base range. A modular type has a base range
whose lower bound is zero, and has operations with ``wraparound'' semantics.
Modular types subsume what are called ``unsigned types'' in some other
- Library unit. A library unit is a separately compiled program unit, and
is always a package, subprogram, or generic unit. Library units may have
other (logically nested) library units as children, and may have other
program units physically nested within them. A root library unit, together
with its children and grandchildren and so on, form a subsystem.
- Limited type. A limited type is (a view of) a type for which the
assignment operation is not allowed. A nonlimited type is a (view of a) type
for which the assignment operation is allowed.
- Object. An object is either a constant or a variable. An object
contains a value. An object is created by an object_declaration or by an
allocator. A formal parameter is (a view of) an object. A subcomponent of
an object is an object.
- Package. Packages are program units that allow the specification of
groups of logically related entities. Typically, a package contains the
declaration of a type (often a private type or private extension) along with
the declarations of primitive subprograms of the type, which can be called
from outside the package, while their inner workings remain hidden from
- Partition. A partition is a part of a program. Each partition consists
of a set of library units. Each partition may run in a separate address
space, possibly on a separate computer. A program may contain just one
partition. A distributed program typically contains multiple partitions,
which can execute concurrently.
- Pragma. A pragma is a compiler directive. There are language-defined
pragmas that give instructions for optimization, listing control, etc. An
implementation may support additional (implementation-defined) pragmas.
- Primitive operations. The primitive operations of a type are the
operations (such as subprograms) declared together with the type declaration.
They are inherited by other types in the same class of types. For a tagged
type, the primitive subprograms are dispatching subprograms, providing
run-time polymorphism. A dispatching subprogram may be called with
statically tagged operands, in which case the subprogram body invoked is
determined at compile time. Alternatively, a dispatching subprogram may be
called using a dispatching call, in which case the subprogram body invoked is
determined at run time.
- Private extension. A private extension is like a record extension,
except that the components of the extension part are hidden from its clients.
- Private type. A private type is a partial view of a type whose full
view is hidden from its clients.
- Program unit. A program unit is either a package, a task unit, a
protected unit, a protected entry, a generic unit, or an explicitly declared
subprogram other than an enumeration literal. Certain kinds of program units
can be separately compiled. Alternatively, they can appear physically nested
within other program units.
- Program. A program is a set of partitions, each of which may execute in
a separate address space, possibly on a separate computer. A partition
consists of a set of library units.
- Protected type. A protected type is a composite type whose components
are protected from concurrent access by multiple tasks.
- Real type. A real type has values that are approximations of the real
numbers. Floating point and fixed point types are real types.
- Record extension. A record extension is a type that extends another
type by adding additional components.
- Record type. A record type is a composite type consisting of zero or
more named components, possibly of different types.
- Scalar type. A scalar type is either a discrete type or a real type.
- Subtype. A subtype is a type together with a constraint, which
constrains the values of the subtype to satisfy a certain condition. The
values of a subtype are a subset of the values of its type.
- Tagged type. The objects of a tagged type have a run-time type tag,
which indicates the specific type with which the object was originally
created. An operand of a class-wide tagged type can be used in a dispatching
call; the tag indicates which subprogram body to invoke. Nondispatching
calls, in which the subprogram body to invoke is determined at compile time,
are also allowed. Tagged types may be extended with additional components.
- Task type. A task type is a composite type whose values are tasks,
which are active entities that may execute concurrently with other tasks.
The top-level task of a partition is called the environment task.
- Type. Each object has a type. A type has an associated set of values,
and a set of primitive operations which implement the fundamental aspects of
its semantics. Types are grouped into classes. The types of a given class
share a set of primitive operations. Classes are closed under derivation;
that is, if a type is in a class, then all of its derivatives are in that
- View. (See Definition.)
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