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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

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formal_array_type_definition ::= array_type_definition

Legality Rules

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The only form of discrete_subtype_definition that is allowed within the declaration of a generic formal (constrained) array subtype is a subtype_mark.
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For a formal array subtype, the actual subtype shall satisfy the following conditions: 
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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.
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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).
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The component subtypes of the formal and actual array types shall statically match.
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If the formal type has aliased components, then so shall the actual. 

Examples

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Example of formal array types: 
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--  given the generic package 
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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;
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--  and the types 
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type Mix    is array (Color range <>) of Boolean;
type Option is array (Color) of Boolean;
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--  then Mix can match Vector and Option can match Table 
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package R is new P(Item   => Boolean, Index => Color,
                   Vector => Mix,     Table => Option);
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--  Note that Mix cannot match Table and Option cannot match Vector
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