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A ParameterizedClass owns a Class definition and a set of formal type
arguments. Those formal type arguments can be used again in that class
definition wherever a class is expected (mainly, these are association
ends and operation argument/return/fault types).
A ParameterizedClass is not a Class and thus cannot be used where a
class can be used. It must be parameterized with a set of actual type
arguments to become usable as a Class. Of course, those actual type
parameters may in turn be formal type parameters defined in the
context of the class where the ParameterizedClassInstantiation is
used. Example:
class Collection<T> extends Iterable<T> {
Here, the "extends Iterable<T>" uses the formal type parameter T as
the type of the actual type parameter in the instantiation of the
ParameterizedClass Iterable<S>. With this it is also possible to
instantiate a type only partially, as in:
class A<S> {
B<S, Integer> b;
class B<T, V> {
The attribute b in class A binds only one of B's type arguments to a
concrete class (Integer). The other is the forwarded formal argument
of A itself.
Regarding conformance, a ParameterizedClass does not conform to
anything because it is not a Class. Only a
ParameterizedClassInstantiation can conform to another class. In this
case, all signatures of the instantiation can be computed but may
still have formal type parameters in them. In this case, conformance
checks can only rely on the type constraints specified for formal type
arguments. They are transitively propagated, as in:
class A<S:Comparable> {
void m(B<S> b) {
In this case, due to the type constraint for A's type argument S, the
signature of m conforms to void m(Comparable).
Type constraints on type arguments can also be inferred from the
implementation. Consider the following example:
class A {
void m(Integer i) { ... }
class B<T> {
A a;
void n(T t) {
In this case the parameter type of A.m (Integer) can be inferred for
the type to which the type of B.n's parameter t has to conform. Since
t's type it T, this establishes a type constraint for T, namely that
it has to conform to Integer.
If multiple such inferences are possible, this will tighten the
constraints for the formal type parameter. If necessary, a new
anonymous Class needs to be constructed for this purpose that contains
the union of all the features required. This could in particular be
implemented by having this new anonymous class maintain delegating
associations to each type that the formal type parameter (T) was used