Ada Reference Manual (Ada 2022) — 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

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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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