3.2.1 Type Declarations
1
A type_declaration declares
a type and its first subtype.
Syntax
2
type_declaration ::= full_type_declaration
|
incomplete_type_declaration
|
private_type_declaration
|
private_extension_declaration
3
full_type_declaration ::=
type defining_identifier [
known_discriminant_part]
is type_definition;
|
task_type_declaration
|
protected_type_declaration
4/2
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type_definition ::=
enumeration_type_definition |
integer_type_definition
|
real_type_definition |
array_type_definition
|
record_type_definition |
access_type_definition
|
derived_type_definition | interface_type_definitionLegality Rules
5
A given type shall not have a subcomponent whose
type is the given type itself.
Static Semantics
6
{first subtype}
The
defining_identifier
of a
type_declaration denotes the
first
subtype of the type. The
known_discriminant_part,
if any, defines the discriminants of the type (see
3.7,
“
Discriminants”). The remainder
of the
type_declaration defines the remaining
characteristics of (the view of) the type.
7/2
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{named type} A
type defined by a
type_declaration is a
named
type; such a type has one or more nameable subtypes.
{anonymous
type} Certain other forms of declaration
also include type definitions as part of the declaration for an object
(including a parameter or a discriminant). The type defined by
such a declaration is
anonymous — it has no nameable subtypes.
{italics (pseudo-names of anonymous types)}
For explanatory purposes, this International Standard
sometimes refers to an anonymous type by a pseudo-name, written in italics,
and uses such pseudo-names at places where the syntax normally requires
an
identifier. For a named type whose first
subtype is T, this International Standard sometimes refers to the type
of T as simply “the type T”.
7.a/2
Ramification: {
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The only user-defined types that can be anonymous in the above sense
are array, access, task, and protected types. An anonymous array, task,
or protected type can be defined as part of an
object_declaration.
An anonymous access type can be defined as part of
numerous
other constructs a parameter or discriminant
specification.
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{full type} A
named type that is declared by a
full_type_declaration,
or an anonymous type that is defined
by an access_definition
or as part of declaring an object of the type, is called a
full
type.
{full type definition}
The declaration of a full
type also declares the full view of the type.{full
view (of a type)} The
type_definition,
task_definition,
protected_definition,
or
access_definition that defines a full type
is called a
full type definition. [Types declared by other forms
of
type_declaration are not separate types;
they are partial or incomplete views of some full type.]
8.a
To be honest: Class-wide, universal,
and root numeric types are full types.
8.b/2
Reason: {
AI95-00230-01}
We need to mention access_definition
separately, as it may occur in renames, which do not declare objects.
9
{predefined operator
[partial]} The definition of a type implicitly
declares certain
predefined operators that operate on the type,
according to what classes the type belongs, as specified in
4.5,
“
Operators and Expression Evaluation”.
9.a
Discussion: We no longer talk about the
implicit declaration of basic operations. These are treated like an if_statement
— they don't need to be declared, but are still applicable to only
certain classes of types.
10
{predefined type}
The
predefined types [(for example the types
Boolean, Wide_Character, Integer,
root_integer, and
universal_integer)]
are the types that are defined in [a predefined library package called]
Standard[; this package also includes the [(implicit)] declarations of
their predefined operators]. [The package Standard is described in
A.1.]
10.a
Ramification: We use the term “predefined”
to refer to entities declared in the visible part of Standard, to implicitly
declared operators of a type whose semantics are defined by the language,
to Standard itself, and to the “predefined environment”.
We do not use this term to refer to library packages other than Standard.
For example Text_IO is a language-defined package, not a predefined package,
and Text_IO.Put_Line is not a predefined operation.
Dynamic Semantics
11
{elaboration (full_type_declaration)
[partial]} The elaboration of a
full_type_declaration
consists of the elaboration of the full type definition.
{elaboration
(full type definition) [partial]} Each
elaboration of a full type definition creates a distinct type and its
first subtype.
11.a
Reason: The creation is associated with
the type definition, rather than the type declaration,
because there are types that are created by full type definitions that
are not immediately contained within a type declaration (e.g. an array
object declaration, a singleton task declaration, etc.).
11.b
Ramification: Any implicit declarations
that occur immediately following the full type definition are elaborated
where they (implicitly) occur.
Examples
12
Examples of type
definitions:
13
(White, Red, Yellow, Green, Blue, Brown, Black)
range 1 .. 72
array(1 .. 10) of Integer
14
Examples of type declarations:
15
type Color is (White, Red, Yellow, Green, Blue, Brown, Black);
type Column is range 1 .. 72;
type Table is array(1 .. 10) of Integer;
16
3 Each of the above examples declares a
named type. The identifier given denotes the first subtype of the type.
Other named subtypes of the type can be declared with
subtype_declarations
(see
3.2.2). Although names do not directly
denote types, a phrase like “the type Column” is sometimes
used in this International Standard to refer to the type of Column, where
Column denotes the first subtype of the type. For an example of the definition
of an anonymous type, see the declaration of the array Color_Table in
3.3.1; its type is anonymous — it has
no nameable subtypes.
Wording Changes from Ada 83
16.a
The syntactic category full_type_declaration
now includes task and protected type declarations.
16.b
We have generalized the concept of first-named
subtype (now called simply “first subtype”) to cover all
kinds of types, for uniformity of description elsewhere. RM83 defined
first-named subtype in Section 13. We define first subtype here, because
it is now a more fundamental concept. We renamed the term, because in
Ada 95 some first subtypes have no name.
16.c/2
{
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We no longer elaborate
discriminant_parts,
because there is nothing to do, and it was complex to say that you only
wanted to elaborate it once for a private or incomplete type. This is
also consistent with the fact that subprogram specifications are not
elaborated (neither in Ada 83 nor in Ada 95). Note, however, that an
access_definition appearing in a
discriminant_part
is elaborated
at the full_type_declaration
(for a nonlimited type) or when an object with such a discriminant
is created
(for a limited type).
Wording Changes from Ada 95
16.d/2
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Added wording so that anonymous access types are
always full types, even if they appear in renames.16.e/2
16.f/2
{
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Added a definition of full view, so that all types
have a well-defined full view.
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