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4.1.3 Selected Components
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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
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selected_component
::= prefix .
selector_name
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selector_name
::= identifier |
character_literal |
operator_symbol
Name Resolution Rules
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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).
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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):
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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:
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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.
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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.
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- 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.
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- 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.
Dynamic Semantics
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The evaluation of a
selected_component
includes the evaluation of the
prefix.
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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
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Examples of
selected components:
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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)
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:
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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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