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4.1.3 Selected Components
1
Selected_components
are used to denote components (including discriminants), entries, entry
families, and protected subprograms; they are also used as expanded names
as described below.
Syntax
2
selected_component
::= prefix .
selector_name
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selector_name
::= identifier |
character_literal |
operator_symbol
Name Resolution Rules
4
A
selected_component
is called an
expanded name if, according to the visibility rules,
at least one possible interpretation of its
prefix
denotes a package or an enclosing named construct (directly, not through
a
subprogram_renaming_declaration
or
generic_renaming_declaration).
5
A selected_component
that is not an expanded name shall resolve to denote one of the following:
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- A component (including a discriminant):
7
The prefix
shall resolve to denote an object or value of some non-array composite
type (after any implicit dereference). The selector_name
shall resolve to denote a discriminant_specification
of the type, or, unless the type is a protected type, a component_declaration
of the type. The selected_component
denotes the corresponding component of the object or value.
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- A single entry, an entry family, or
a protected subprogram:
9
The prefix
shall resolve to denote an object or value of some task or protected
type (after any implicit dereference). The selector_name
shall resolve to denote an entry_declaration
or subprogram_declaration occurring
(implicitly or explicitly) within the visible part of that type. The
selected_component denotes the corresponding
entry, entry family, or protected subprogram.
9.1/2
- A view of a subprogram whose first
formal parameter is of a tagged type or is an access parameter whose
designated type is tagged:
9.2/2
The prefix
(after any implicit dereference) shall resolve to denote an object or
value of a specific tagged type T or class-wide type T'Class.
The selector_name shall resolve
to denote a view of a subprogram declared immediately within the declarative
region in which an ancestor of the type T is declared. The first
formal parameter of the subprogram shall be of type T, or a class-wide
type that covers T, or an access parameter designating one of
these types. The designator of the subprogram shall not be the same as
that of a component of the tagged type visible at the point of the selected_component.
The selected_component denotes a
view of this subprogram that omits the first formal parameter. This view
is called a prefixed view of the subprogram, and the prefix
of the selected_component (after
any implicit dereference) is called the prefix of the prefixed
view.
10
An expanded name
shall resolve to denote a declaration that occurs immediately within
a named declarative region, as follows:
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- The prefix
shall resolve to denote either a package (including the current instance
of a generic package, or a rename of a package), or an enclosing named
construct.
12
- The selector_name
shall resolve to denote a declaration that occurs immediately within
the declarative region of the package or enclosing construct (the declaration
shall be visible at the place of the expanded name — see 8.3).
The expanded name denotes that declaration.
13
- If the prefix
does not denote a package, then it shall be a direct_name
or an expanded name, and it shall resolve to denote a program unit (other
than a package), the current instance of a type, a block_statement,
a loop_statement, or an accept_statement
(in the case of an accept_statement
or entry_body, no family index is
allowed); the expanded name shall occur within the declarative region
of this construct. Further, if this construct is a callable construct
and the prefix denotes more than
one such enclosing callable construct, then the expanded name is ambiguous,
independently of the selector_name.
Legality Rules
13.1/2
For a subprogram whose first parameter is
an access parameter, the prefix of any prefixed view shall denote an
aliased view of an object.
13.2/2
For a subprogram whose first parameter is
of mode in out or out, or of an anonymous access-to-variable
type, the prefix of any prefixed view shall denote a variable.
Dynamic Semantics
14
The evaluation of a
selected_component
includes the evaluation of the
prefix.
15
For a
selected_component that denotes
a component of a
variant, a check
is made that the values of the discriminants are such that the value
or object denoted by the
prefix
has this component.
The exception
Constraint_Error is raised if this check fails.
Examples
16
Examples of
selected components:
17/2
Tomorrow.Month -- a record component (see 3.8)
Next_Car.Owner -- a record component (see 3.10.1)
Next_Car.Owner.Age -- a record component (see 3.10.1)
-- the previous two lines involve implicit dereferences
Writer.Unit -- a record component (a discriminant) (see 3.8.1)
Min_Cell(H).Value -- a record component of the result (see 6.1)
-- of the function call Min_Cell(H)
Cashier.Append -- a prefixed view of a procedure (see 3.9.4)
Control.Seize -- an entry of a protected object (see 9.4)
Pool(K).Write -- an entry of the task Pool(K) (see 9.4)
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Examples of expanded
names:
19
Key_Manager."<" -- an operator of the visible part of a package (see 7.3.1)
Dot_Product.Sum -- a variable declared in a function body (see 6.1)
Buffer.Pool -- a variable declared in a protected unit (see 9.11)
Buffer.Read -- an entry of a protected unit (see 9.11)
Swap.Temp -- a variable declared in a block statement (see 5.6)
Standard.Boolean -- the name of a predefined type (see A.1)
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