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
   

3. 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:
   1. A component (including a discriminant):
      1. 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.

1. A single entry, an entry family, or a protected subprogram:
   1. 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.

1. An expanded name shall resolve to denote a declaration that occurs immediately within a named declarative region, as follows:
   1. 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.
   2. 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 section 8.3 Visibility.). The expanded name denotes that declaration.
   3. 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.

1. The evaluation of a selected_component includes the evaluation of the prefix.
2. 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
   
3. Examples of selected components:

4. Tomorrow.Month
   --  a record component                   See section 3.8 Record Types
   
   Next_Car.Owner
   --  a record component                   See section 3.10.1 Incomplete Type Declarations
   
   Next_Car.Owner.Age
   --  a record component                   See section 3.10.1 Incomplete Type Declarations
   --  the previous two lines involve implicit dereferences
   
   Writer.Unit
   --  a record component (a discriminant)  See section 3.8.1 Variant Parts and Discrete Choices
   
   Min_Cell(H).Value
   --  a record component of the result     See section 6.1 Subprogram Declarations
   --  of the function call Min_Cell(H)
   
   Control.Seize
   --  an entry of a protected object       See section 9.4 Protected Units and Protected Objects
   
   Pool(K).Write
   --  an entry of the task Pool(K)         See section 9.4 Protected Units and Protected Objects
   

5. Examples of expanded names:

6. Key_Manager."<"
   --  an operator of the visible part of a package  See section 7.3.1 Private Operations
   
   Dot_Product.Sum
   --  a variable declared in a function body        See section 6.1 Subprogram Declarations
   
   Buffer.Pool
   --  a variable declared in a protected unit       See section 9.11 Example of Tasking and Synchronization
   
   Buffer.Read
   --  an entry of a protected unit                  See section 9.11 Example of Tasking and Synchronization
   
   Swap.Temp
   --  a variable declared in a block statement      See section 5.6 Block Statements
   
   Standard.Boolean
   --  the name of a predefined type                 See section A.1 The Package Standard
   

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