Ada Reference Manual (Ada 2022) — Legal Information

8.5.1 Object Renaming Declarations

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An object_renaming_declaration is used to rename an object or value.

Syntax

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object_renaming_declaration ::=
    defining_identifier [: [null_exclusion] subtype_mark] renames object_name
        [aspect_specification];
  | defining_identifier : access_definition renames object_name
        [aspect_specification];

Name Resolution Rules

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The type of the object_name shall resolve to the type determined by the subtype_mark, if present. If no subtype_mark or access_definition is present, the expected type of the object_name is any type.

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In the case where the type is defined by an access_definition, the type of the object_name shall resolve to an anonymous access type. If the anonymous access type is an access-to-object type, the type of the object_name shall have the same designated type as that of the access_definition. If the anonymous access type is an access-to-subprogram type, the type of the object_name shall have a designated profile that is type conformant with that of the access_definition.

Legality Rules

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The renamed entity shall be an object or value.

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In the case where the type is defined by an access_definition, the type of the renamed entity and the type defined by the access_definition:

4.2/2

shall both be access-to-object types with statically matching designated subtypes and with both or neither being access-to-constant types; or

4.3/2

shall both be access-to-subprogram types with subtype conformant designated profiles.

4.4/5

For an object_renaming_declaration with a null_exclusion or an access_definition that has a null_exclusion, the subtype of the object_name shall exclude null. In addition, if the object_renaming_declaration occurs within the body of a generic unit G or within the body of a generic unit declared within the declarative region of generic unit G, then:

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if the object_name statically denotes a generic formal object of mode in out of G, then the declaration of that object shall have a null_exclusion;

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if the object_name statically denotes a call of a generic formal function of G, then the declaration of the result of that function shall have a null_exclusion.

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In the case where the object_name is a qualified_expression with a nominal subtype S and whose expression is a name that denotes an object Q:

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if S is an elementary subtype, then:

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Q shall be a constant other than a dereference of an access type; or

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the nominal subtype of Q shall be statically compatible with S; or

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S shall statically match the base subtype of its type if scalar, or the first subtype of its type if an access type.

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if S is a composite subtype, then Q shall be known to be constrained or S shall statically match the first subtype of its type.

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The renamed entity shall not be a subcomponent that depends on discriminants of an object whose nominal subtype is unconstrained unless the object is known to be constrained. A slice of an array shall not be renamed if this restriction disallows renaming of the array.

5.1/5

In addition to the places where Legality Rules normally apply (see 12.3), these rules also apply in the private part of an instance of a generic unit.

Static Semantics

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An object_renaming_declaration declares a new view of the renamed entity whose properties are identical to those of the renamed view. Thus, the properties of the renamed entity are not affected by the renaming_declaration. In particular, its nominal subtype, whether it is a value or an object, its value if it is an object, and whether or not it is a constant, are unaffected; similarly, the constraints and other properties of its nominal subtype are not affected by renaming (any constraint implied by the subtype_mark or access_definition of the object_renaming_declaration is ignored).

Examples

Example of renaming an object:

declare
L : Person renames Leftmost_Person; -- see 3.10.1
begin
L.Age := L.Age + 1;
end;

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Example of renaming a value:

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Uno renames One; -- see 3.3.2

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