This Annex contains informal descriptions of some
of the terms used in this Reference Manual. The index provides references
to more formal definitions of all of the terms used in this Reference
type is a tagged type intended for use as an ancestor of other types,
but which is not allowed to have objects of its own.
type has values that designate aliased objects. Access types correspond
to “pointer types” or “reference types” in some
level. An accessibility level is a representation
of the lifetime of an entity in terms of the level of dynamic nesting
within which the entity is known to exist. Dynamic accessibility checks
ensure that a reference does not outlive the entity to which it refers,
by checking that the level of the entity is no deeper than the level
of the reference. Based on static nesting, there are corresponding legality
rules that the level of the entity is not statically deeper than that
of the reference.
An aggregate is a construct used to define a value
of a composite type by specifying the values of the components of the
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 object.
of a type is the type itself or, in the case of a type derived from other
types, its parent type or one of its progenitor types or one of their
ancestors. Note that ancestor and descendant are inverse relationships.
type is a composite type whose components are all of the same type. Components
are selected by indexing.
An aspect is
a specifiable property of an entity. An aspect may be specified by an
on the declaration of the entity. Some aspects may be queried via attributes.
is a boolean expression that appears in any of the following: a pragma
Assert, a predicate, a precondition, a postcondition, an invariant, a
constraint, or a null exclusion. An assertion is expected to be True
at run time at certain specified places.
An attribute is a characteristic or property of
an entity that can be queried, and in some cases specified.
Category (of types).
A category of types is a set of types with one or more common properties,
such as primitive operations. A category of types that is closed under
derivation is also known as a class
type is an enumeration type whose values include characters.
A check is a test made during execution to determine
whether a language rule has been violated.
Class (of types).
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.
type may have components.
is a piece of text (explicit or implicit) that is an instance of a syntactic
category defined under “Syntax”.
is an object that contain other objects all of the same type, which could
be class-wide. Several predefined container types are provided by the
children of package Ada.Containers (see A.18.1
aggregate. A container aggregate is
a construct used to define a value of a type that represents a collection
of elements, by explicitly specifying the elements in the collection.
type supports user-defined assignment and finalization. Objects are always
finalized before being destroyed.
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
initial condition. A default initial
condition is a property that holds for every default-initialized object
of a given type.
This paragraph was
type is a type defined in terms of one or more other types given in a
derived type definition. The first of those types is the parent type
of the derived type and any others are progenitor types. Each class containing
the parent type or a progenitor type also contains the derived type.
The derived type inherits properties such as components and primitive
operations from the parent and progenitors. A type together with the
types derived from it (directly or indirectly) form a derivation class.
is a descendant of itself, its parent and progenitor types, and their
ancestors. Note that descendant and ancestor are inverse relationships.
type is either an integer type or an enumeration type. Discrete types
may be used, for example, in case_statement
and as array indices.
is a parameter for a composite type. It can control, for example, the
bounds of a component of the type if the component is an array. A discriminant
for a task type can be used to pass data to a task of the type upon creation.
by which a declaration achieves its run-time effect is called elaboration.
Elaboration is one of the forms of execution.
type is a type that
does not have components.
enumeration type is defined by an enumeration of its values, which may
be named by identifiers or character literals.
by which an expression achieves its run-time effect is called evaluation.
Evaluation is one of the forms of execution.
represents a kind of exceptional situation; an occurrence of such a situation
(at run time) is called an exception occurrence
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
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
is a form of subprogram that returns a result and can be called as part
of an expression.
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 sometimes play in other languages.
incomplete type gives a view of a type that reveals only some of its
properties. The remaining properties are provided by the full view given
elsewhere. Incomplete types can be used for defining recursive data structures.
Indexable container type.
An indexable container type is one that has user-defined behavior for
indexing, via the Constant_Indexing or Variable_Indexing aspects.
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 languages.
interface type is a form of abstract tagged type which has no components
or concrete operations except possibly null procedures. Interface types
are used for composing other interfaces and tagged types and thereby
provide multiple inheritance. Only an interface type can be used as a
progenitor of another type.
is an assertion that is expected to be True for all objects of a given
private type when viewed from outside the defining package.
Iterable container type.
An iterable container type is one that has user-defined behavior for
iteration, via the Default_Iterator and Iterator_Element aspects.
is a construct that is used to loop over the elements of an array or
container. Iterators may be user defined, and may perform arbitrary computations
to access elements from a container.
filter. An iterator filter is a construct
that is used to restrict the elements produced by an iteration to those
for which a boolean condition evaluates to True.
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.
library unit, together with its children and grandchildren and so on,
form a subsystem
type is a type for which copying (such as in an assignment_statement
is not allowed. A nonlimited type is a type for which copying is allowed.
thread of control. A logical thread
of control is an activity within the execution of a program that can
proceed in parallel with other activities of the same task, or of separate
A master is the execution of a master construct.
Each object and task is associated with a master. When a master is left,
associated tasks are awaited and associated objects are finalized.
construct. A master construct is one
of certain executable constructs listed in 7.6.1.
Execution of a master construct is a master, with which objects and tasks
are associated for the purposes of waiting and finalization.
subtype. The nominal subtype of a view
of an object is the subtype specified when the view is defined.
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.
aspect. An operational aspect is an
aspect that indicates a logical property of an entity, such as the precondition
of a subprogram, or the procedure used to write a given type of object
to a stream.
An overriding operation is one that replaces an inherited primitive operation.
Operations may be marked explicitly as overriding or not overriding.
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 outside users.
construct. A parallel construct is an
executable construct that defines multiple activities of a single task
that can proceed in parallel, via the execution of multiple logical threads
of a derived type is the first type given in the definition of the derived
type. The parent can be almost any kind of type, including an interface
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.
is an assertion that is expected to be True when a given subprogram returns
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.
is an assertion that is expected to be True when a given subprogram is
is an assertion that is expected to be True for all objects of a given
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 is a type that extends another type, with the additional
properties hidden from its clients.
type gives a view of a type that reveals only some of its properties.
The remaining properties are provided by the full view given elsewhere.
Private types can be used for defining abstractions that hide unnecessary
details from their clients.
is a form of subprogram that does not return a result and can only be
called by a statement
of a derived type is one of the types given in the definition of the
derived type other than the first. A progenitor is always an interface
type. Interfaces, tasks, and protected types may also have progenitors.
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.
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
type is a composite type whose components are accessible only through
one of its protected operations which synchronize concurrent access by
A real type
has values that are approximations of the real numbers. Floating point
and fixed point types are real types.
extension is a type that extends another type by adding additional components.
type is a composite type consisting of zero or more named components,
possibly of different types.
expression. A reduction expression is
an expression that defines how to map or transform a collection of values
into a new set of values, and then summarize the values by applying an
operation to reduce the set to a single value.
type is one that has user-defined behavior for “.all
defined by the Implicit_Dereference aspect.
is a declaration that does not define a new entity, but instead defines
a view of an existing entity.
aspect. A representation aspect is an
aspect that indicates how an entity is mapped onto the underlying hardware,
for example the size or alignment of an object.
type is either a discrete type or a real type.
property. A stable property is a characteristic
associated with objects of a given type that is preserved by many of
the primitive operations of the type.
access-to-object type has an associated storage pool object. The storage
for an object created by an allocator
comes from the storage pool of the type of the allocator
Some storage pools may be partitioned into subpools in order to support
finer-grained storage management.
A stream is
a sequence of elements that can be used, along with the stream-oriented
attributes, to support marshalling and unmarshalling of values of most
is a section of a program that can be executed in various contexts. It
is invoked by a subprogram call that may qualify the effect of the subprogram
through the passing of parameters. There are two forms of subprograms:
functions, which return values, and procedures, which do not.
A subtype is
a type together with optional constraints, null exclusions, and predicates,
which constrain the values of the subtype to satisfy certain conditions.
The values of a subtype are a subset of the values of its type.
A subunit is a body of a program unit that can
be compiled separately from its enclosing program unit.
To suppress a check is to assert that the check
cannot fail, and to request that the compiler optimize by disabling the
check. The compiler is not required to honor this request. Suppressing
checks that can fail can cause a program to behave in arbitrary ways.
entity is one that will work safely with multiple tasks at one time.
A synchronized interface can be an ancestor of a task or a protected
type. Such a task or protected type is called a synchronized tagged type.
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.
A task type
is a composite type used to represent active entities which execute concurrently
and which can communicate via queued task entries. The top-level task
of a partition is called the environment task.
Each object has
a type. A type
has an associated set of values, and a set of primitive
which implement the fundamental aspects of its semantics.
Types are grouped into categories
. Most language-defined categories
of types are also classes
invariant. See Invariant.
A view of an entity
reveals some or all of the properties of the entity. A single entity
may have multiple views.
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