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- (1)
- A record type with a variant_part specifies alternative lists of components. Each variant defines the components for the value or values of the discriminant covered by its discrete_choice_list.

(2) variant_part ::= case discriminant_direct_name is variant {variant} end case; (3) variant ::= when discrete_choice_list => component_list (4) discrete_choice_list ::= discrete_choice {| discrete_choice} (5) discrete_choice ::= expression | discrete_range | others

- (6)
- The discriminant_direct_name shall resolve to denote a discriminant (called the discriminant of the variant_part) specified in the known_discriminant_part of the full_type_declaration that contains the variant_part. The expected type for each discrete_choice in a variant is the type of the discriminant of the variant_part.

- (7)
- The discriminant of the variant_part shall be of a discrete type.
- (8)
- The expressions and discrete_ranges given as discrete_choices in a variant_part shall be static. The discrete_choice others shall appear alone in a discrete_choice_list, and such a discrete_choice_list, if it appears, shall be the last one in the enclosing construct.
- (9)
- A discrete_choice is defined to cover a value in the following cases:
- (10)
- A discrete_choice that is an expression covers a value if the value equals the value of the expression converted to the expected type.

- (11)
- A discrete_choice that is a discrete_range covers all values (possibly none) that belong to the range.

- (12)
- The discrete_choice others covers all values of its expected type that are not covered by previous discrete_choice_lists of the same construct.

- (13)
- A discrete_choice_list covers a value if one of its discrete_choices covers the value.
- (14)
- The possible values of the discriminant of a variant_part shall be covered as follows:
- (15)
- If the discriminant is of a static constrained scalar subtype, then each non-others discrete_choice shall cover only values in that subtype, and each value of that subtype shall be covered by some discrete_choice (either explicitly or by others);

- (16)
- If the type of the discriminant is a descendant of a generic formal scalar type then the variant_part shall have an others discrete_choice;

- (17)
- Otherwise, each value of the base range of the type of the discriminant shall be covered (either explicitly or by others).

- (18)
- Two distinct discrete_choices of a variant_part shall not cover the same value.

- (19)
- If the component_list of a variant is specified by null, the variant has no components.
- (20)
- The discriminant of a variant_part is said to govern the variant_part and its variants. In addition, the discriminant of a derived type governs a variant_part and its variants if it corresponds (see 3.7) to the discriminant of the variant_part.

- (21)
- A record value contains the values of the components of a particular variant only if the value of the discriminant governing the variant is covered by the discrete_choice_list of the variant. This rule applies in turn to any further variant that is, itself, included in the component_list of the given variant.
- (22)
- The elaboration of a variant_part consists of the elaboration of the component_list of each variant in the order in which they appear.

- (23)
*Example of record type with a variant part:*

(24) type Device is (Printer, Disk, Drum); type State is (Open, Closed); (25) type Peripheral(Unit : Device := Disk) is record Status : State; case Unit is when Printer => Line_Count : Integer range 1 .. Page_Size; when others => Cylinder : Cylinder_Index; Track : Track_Number; end case; end record;

- (26)
*Examples of record subtypes:*

(27) subtype Drum_Unit is Peripheral(Drum); subtype Disk_Unit is Peripheral(Disk);

- (28)
*Examples of constrained record variables:*

(29) Writer : Peripheral(Unit => Printer); Archive : Disk_Unit;

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