Ada Reference Manual — Legal Information

12.5.3 Formal Array Types

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The category determined for a formal array type is the category of all array types.

Syntax

formal_array_type_definition ::= array_type_definition

Legality Rules

The only form of discrete_subtype_definition that is allowed within the declaration of a generic formal (constrained) array subtype is a subtype_mark.

For a formal array subtype, the actual subtype shall satisfy the following conditions:

The formal array type and the actual array type shall have the same dimensionality; the formal subtype and the actual subtype shall be either both constrained or both unconstrained.

For each index position, the index types shall be the same, and the index subtypes (if unconstrained), or the index ranges (if constrained), shall statically match (see 4.9.1).

The component subtypes of the formal and actual array types shall statically match.

If the formal type has aliased components, then so shall the actual.

Examples

Example of formal array types:

-- given the generic package

generic
   type Item   is private;
   type Index  is (<>);
   type Vector is array (Index range <>) of Item;
   type Table  is array (Index) of Item;
package P is
   ...
end P;

-- and the types

type Mix is array (Color range <>) of Boolean;
type Option is array (Color) of Boolean;

-- then Mix can match Vector and Option can match Table

package R is new P(Item => Boolean, Index => Color,
Vector => Mix, Table => Option);

-- Note that Mix cannot match Table and Option cannot match Vector