12.4 Formal Objects
A generic formal object can be used to pass a value or variable to a generic unit.
formal_object_declaration ::= defining_identifier_list : mode subtype_mark [:= default_expression];
Name Resolution Rules
The expected type for the default_expression, if any, of a formal object is the type of the formal object.
For a generic formal object of mode in, the expected type for the actual is the type of the formal.
For a generic formal object of mode in out, the type of the actual shall resolve to the type of the formal.
If a generic formal object has a default_expression, then the mode shall be in (either explicitly or by default); otherwise, its mode shall be either in or in out.
For a generic formal object of mode in, the actual shall be an expression. For a generic formal object of mode in out, the actual shall be a name that denotes a variable for which renaming is allowed (see 8.5.1).
The type of a generic formal object of mode in shall be nonlimited.
A formal_object_declaration declares a generic formal object. The default mode is in. For a formal object of mode in, the nominal subtype is the one denoted by the subtype_mark in the declaration of the formal. For a formal object of mode in out, its type is determined by the subtype_mark in the declaration; its nominal subtype is nonstatic, even if the subtype_mark denotes a static subtype.
In an instance, a formal_object_declaration of mode in declares a new stand-alone constant object whose initialization expression is the actual, whereas a formal_object_declaration of mode in out declares a view whose properties are identical to those of the actual.
For the evaluation of a generic_association for a formal object of mode in, a constant object is created, the value of the actual parameter is converted to the nominal subtype of the formal object, and assigned to the object, including any value adjustment -- see 7.6.
6 The constraints that apply to a generic formal object of mode in out are those of the corresponding generic actual parameter (not those implied by the subtype_mark that appears in the formal_object_declaration). Therefore, to avoid confusion, it is recommended that the name of a first subtype be used for the declaration of such a formal object.
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Copyright © 2000 The MITRE Corporation, Inc. Ada Reference Manual