Ada Reference ManualLegal Information
Contents   Index   References   Search   Previous   Next 

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:
6
7
8
9
9.1/2
9.2/2
10
An expanded name shall resolve to denote a declaration that occurs immediately within a named declarative region, as follows: 
11
12
13

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)
18
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)






Contents   Index   References   Search   Previous   Next 
Ada-Europe Sponsored by Ada-Europe