10.1.1 Compilation Units - Library Units
1
A
library_item is a compilation
unit that is the declaration, body, or renaming of a library unit. Each
library unit (except Standard) has a
parent unit, which is a library
package or generic library package.
A library unit
is a
child of its parent unit. The
root library units are
the children of the predefined library package Standard.
Syntax
2
compilation ::= {
compilation_unit}
3
compilation_unit ::=
context_clause library_item
|
context_clause subunit
4
library_item ::= [
private]
library_unit_declaration
|
library_unit_body
| [
private]
library_unit_renaming_declaration
5
library_unit_declaration ::=
subprogram_declaration |
package_declaration
|
generic_declaration |
generic_instantiation
6
library_unit_renaming_declaration ::=
package_renaming_declaration
|
generic_renaming_declaration
|
subprogram_renaming_declaration
7
library_unit_body ::= subprogram_body |
package_body
8
parent_unit_name ::= name
8.1/2
An overriding_indicator
is not allowed in a subprogram_declaration,
generic_instantiation, or subprogram_renaming_declaration
that declares a library unit.
9
A
library unit is a program unit that is declared by a
library_item.
When a program unit is a library unit, the prefix “library”
is used to refer to it (or “generic library” if generic),
as well as to its declaration and body, as in “library procedure”,
“library
package_body”, or “generic
library package”.
The term
compilation unit
is used to refer to a
compilation_unit. When
the meaning is clear from context, the term is also used to refer to
the
library_item of a
compilation_unit
or to the
proper_body of a
subunit
(that is, the
compilation_unit without the
context_clause and the
separate (
parent_unit_name)).
10
The
parent
declaration of a
library_item (and of
the library unit) is the declaration denoted by the
parent_unit_name,
if any, of the
defining_program_unit_name
of the
library_item.
If
there is no
parent_unit_name, the parent declaration
is the declaration of Standard, the
library_item
is a
root library_item, and the library
unit (renaming) is a
root library unit (renaming). The declaration
and body of Standard itself have no parent declaration.
The
parent unit of a
library_item or library
unit is the library unit declared by its parent declaration.
11
The children of a library unit occur immediately
within the declarative region of the declaration of the library unit.
The
ancestors of a library unit are itself,
its parent, its parent's parent, and so on. (Standard is an ancestor
of every library unit.)
The
descendant relation
is the inverse of the ancestor relation.
12
A
library_unit_declaration or a
library_unit_renaming_declaration
is
private if the declaration is immediately preceded by the reserved
word
private; it is otherwise
public. A library unit is
private or public according to its declaration.
The
public descendants of a library unit are the library unit itself,
and the public descendants of its public children.
Its
other descendants are
private descendants.
12.1/2
For each library
package_declaration
in the environment, there is an implicit declaration of a
limited
view of that library package.
The limited view
of a package contains:
12.2/2
- For each nested package_declaration,
a declaration of the limited view of that package, with the same defining_program_unit_name.
12.3/2
- For each type_declaration
in the visible part, an incomplete view of the type; if the type_declaration
is tagged, then the view is a tagged incomplete view.
12.4/2
The limited view of a library package_declaration
is private if that library package_declaration
is immediately preceded by the reserved word private.
12.5/2
There is no syntax for declaring limited views
of packages, because they are always implicit. The implicit declaration
of a limited view of a library package is not the declaration of a library
unit (the library package_declaration is);
nonetheless, it is a library_item. The implicit
declaration of the limited view of a library package forms an (implicit)
compilation unit whose context_clause is empty.
12.6/2
A library package_declaration
is the completion of the declaration of its limited view.
Legality Rules
13
The parent unit of a library_item
shall be a library package or generic library package.
14
If a defining_program_unit_name
of a given declaration or body has a parent_unit_name,
then the given declaration or body shall be a library_item.
The body of a program unit shall be a library_item
if and only if the declaration of the program unit is a library_item.
In a library_unit_renaming_declaration, the
(old) name shall denote a library_item.
15/2
A parent_unit_name (which
can be used within a defining_program_unit_name
of a library_item and in the separate
clause of a subunit), and each of its prefixes,
shall not denote a renaming_declaration. On
the other hand, a name that denotes a library_unit_renaming_declaration
is allowed in a nonlimited_with_clause and
other places where the name of a library unit is allowed.
16
If a library package is an instance of a generic
package, then every child of the library package shall either be itself
an instance or be a renaming of a library unit.
17
A child of a generic library package shall either
be itself a generic unit or be a renaming of some other child of the
same generic unit. The renaming of a child of a generic package shall
occur only within the declarative region of the generic package.
18
A child of a parent generic package shall be instantiated
or renamed only within the declarative region of the parent generic.
19/2
For each child C of some parent generic package
P, there is a corresponding declaration C nested immediately
within each instance of P. For the purposes of this rule, if a
child C itself has a child D, each corresponding declaration
for C has a corresponding child D. The corresponding declaration
for a child within an instance is visible only within the scope of a
with_clause that mentions the (original) child
generic unit.
20
A library subprogram shall not override a primitive
subprogram.
21
The defining name of a function that is a compilation
unit shall not be an operator_symbol.
Static Semantics
22
A subprogram_renaming_declaration
that is a library_unit_renaming_declaration
is a renaming-as-declaration, not a renaming-as-body.
23
There are two kinds
of dependences among compilation units:
24
- The semantic dependences (see
below) are the ones needed to check the compile-time rules across compilation
unit boundaries; a compilation unit depends semantically on the other
compilation units needed to determine its legality. The visibility rules
are based on the semantic dependences.
25
- The elaboration dependences
(see 10.2) determine the order of elaboration
of library_items.
26/2
A
library_item
depends semantically upon its parent declaration. A subunit depends semantically
upon its parent body. A
library_unit_body
depends semantically upon the corresponding
library_unit_declaration,
if any. The declaration of the limited view of a library package depends
semantically upon the declaration of the limited view of its parent.
The declaration of a library package depends semantically upon the declaration
of its limited view. A compilation unit depends semantically upon each
library_item mentioned in a
with_clause
of the compilation unit. In addition, if a given compilation unit contains
an
attribute_reference of a type defined in
another compilation unit, then the given compilation unit depends semantically
upon the other compilation unit. The semantic dependence relationship
is transitive.
Dynamic Semantics
26.1/2
The elaboration of the declaration of the limited
view of a package has no effect.
27
1 A simple program may consist of a single
compilation unit. A compilation need not have
any compilation units; for example, its text can consist of pragmas.
28
2 The designator
of a library function cannot be an operator_symbol,
but a nonlibrary renaming_declaration is allowed
to rename a library function as an operator. Within a partition, two
library subprograms are required to have distinct names and hence cannot
overload each other. However, renaming_declarations
are allowed to define overloaded names for such subprograms, and a locally
declared subprogram is allowed to overload a library subprogram. The
expanded name Standard.L can be used to denote a root library unit L
(unless the declaration of Standard is hidden) since root library unit
declarations occur immediately within the declarative region of package
Standard.
Examples
29
Examples of library
units:
30
package Rational_Numbers.IO
is --
public child of Rational_Numbers, see 7.1
procedure Put(R :
in Rational);
procedure Get(R :
out Rational);
end Rational_Numbers.IO;
31
private procedure Rational_Numbers.Reduce(R : in out Rational);
-- private child of Rational_Numbers
32
with Rational_Numbers.Reduce; -- refer to a private child
package body Rational_Numbers is
...
end Rational_Numbers;
33
with Rational_Numbers.IO;
use Rational_Numbers;
with Ada.Text_io; --
see A.10
procedure Main
is --
a root library procedure
R : Rational;
begin
R := 5/3; --
construct a rational number, see 7.1
Ada.Text_IO.Put("The answer is: ");
IO.Put(R);
Ada.Text_IO.New_Line;
end Main;
34
with Rational_Numbers.IO;
package Rational_IO renames Rational_Numbers.IO;
-- a library unit renaming declaration
35
Each of the above library_items
can be submitted to the compiler separately.
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