- The class determined for a formal private type can be either limited or
nonlimited, and either tagged or untagged; no more specific class is known
for such a type. The class determined for a formal derived type is the
derivation class rooted at the ancestor type.
formal_private_type_definition ::= [[abstract] tagged] [limited] private
formal_derived_type_definition ::= [abstract] new subtype_mark [with private]
- If a generic formal type declaration has a known_discriminant_part, then
it shall not include a default_expression for a discriminant.
- The ancestor subtype of a formal derived type is the subtype denoted by
the subtype_mark of the formal_derived_type_definition. For a formal derived
type declaration, the reserved words with private shall appear if and only if
the ancestor type is a tagged type; in this case the formal derived type is a
private extension of the ancestor type and the ancestor shall not be a
class-wide type. Similarly, the optional reserved word abstract shall appear
only if the ancestor type is a tagged type.
- If the formal subtype is definite, then the actual subtype shall also be
- For a generic formal derived type with no discriminant_part:
- If the ancestor subtype is constrained, the actual subtype shall
be constrained, and shall be statically compatible with the
- If the ancestor subtype is an unconstrained access or composite
subtype, the actual subtype shall be unconstrained.
- If the ancestor subtype is an unconstrained discriminated subtype, then
the actual shall have the same number of discriminants, and each discriminant
of the actual shall correspond to a discriminant of the ancestor, in the
sense of 3.7.
- The declaration of a formal derived type shall not have a known_discriminant_part. For a generic formal private type with a known_discriminant_part:
- The actual type shall be a type with the same number of
- The actual subtype shall be unconstrained.
- The subtype of each discriminant of the actual type shall
statically match the subtype of the corresponding discriminant of
the formal type.
- For a generic formal type with an unknown_discriminant_part, the actual
may, but need not, have discriminants, and may be definite or indefinite.
- The class determined for a formal private type is as follows:
Type Definition Determined Class
limited private the class of all types
private the class of all nonlimited types
tagged limited private the class of all tagged types
tagged private the class of all nonlimited tagged types
- The presence of the reserved word abstract determines whether the actual
type may be abstract.
- A formal private or derived type is a private or derived type,
respectively. A formal derived tagged type is a private extension. A formal
private or derived type is abstract if the reserved word abstract appears in
- If the ancestor type is a composite type that is not an array type, the
formal type inherits components from the ancestor type (including discriminants
if a new discriminant_part is not specified), as for a derived type defined
by a derived_type_definition (see 3.4).
- For a formal derived type, the predefined operators and inherited user-defined
subprograms are determined by the ancestor type, and are implicitly declared
at the earliest place, if any, within the immediate scope of the formal type,
where the corresponding primitive subprogram of the ancestor is visible (see
7.3.1). In an instance, the copy of such an implicit declaration declares
a view of the corresponding primitive subprogram of the ancestor, even if
this primitive has been overridden for the actual type. In the case of a formal
private extension, however, the tag of the formal type is that of the actual
type, so if the tag in a call is statically determined to be that of the formal
type, the body executed will be that corresponding to the actual type.
- For a prefix S that denotes a formal indefinite subtype, the following
attribute is defined:
S'Definite yields True if the actual subtype corresponding to
S is definite; otherwise it yields False. The value of this
attribute is of the predefined type Boolean.
(9) In accordance with the general rule that the actual type shall belong
to the class determined for the formal (see 12.5,
- If the formal type is nonlimited, then so shall be the
- For a formal derived type, the actual shall be in the class
rooted at the ancestor subtype.
(10) The actual type can be abstract only if the formal type is abstract
(11) If the formal has a discriminant_part, the actual can be either
definite or indefinite. Otherwise, the actual has to be definite.
-- Email comments, additions, corrections, gripes, kudos, etc. to:
Magnus Kempe -- Magnus.Kempe@di.epfl.ch
Page last generated: 95-03-12