4.1.3 Selected Components
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.
selected_component ::= prefix . selector_name
selector_name ::= identifier | character_literal | operator_symbol
Name Resolution Rules
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).
A selected_component that is not an expanded name shall resolve to denote one of the following:
- A component (including a discriminant):
- 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.
- A single entry, an entry family, or a protected subprogram:
- 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.
An expanded name shall resolve to denote a declaration that occurs immediately within a named declarative region, as follows:
- 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.
- 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.
- 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.
The evaluation of a selected_component includes the evaluation of the prefix.
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 of selected components:
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)
Examples of expanded names:
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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Copyright © 2000 The MITRE Corporation, Inc. Ada Reference Manual