Java Reference
In-Depth Information
that are known to be supertypes of
T
j
. This will be our candidate invocation of
G
in
the bound we infer for
T
j
.
Define CandidateInvocation(
G
) = lci(Inv(
G
)), where lci, the least containing invocation, is
defined:
• lci(
S
) = lci(
e
1
, ...,
e
n
) where
e
i
(1 ≤
i
≤
n
) in
S
• lci(
e
1
, ...,
e
n
) = lci(lci(
e
1
,
e
2
),
e
3
, ...,
e
n
)
• lci(
G
<
X
1
, ...,
X
n
>
,
G
<
Y
1
, ...,
Y
n
>
) =
G
<
lcta(
X
1
,
Y
1
), ..., lcta(
X
n
,
Y
n
)
>
• lci(
G
<
X
1
, ...,
X
n
>
) =
G
<
lcta(
X
1
), ..., lcta(
X
n
)
>
where lcta() is the least containing type argument function defined (assuming
U
and
V
are
type expressions) as:
• lcta(
U
,
V
) =
U
if
U
=
V
, otherwise
? extends
lub(
U
,
V
)
• lcta(
U
,
? extends
V
) =
? extends
lub(
U
,
V
)
• lcta(
U
,
? super
V
) =
? super
glb(
U
,
V
)
• lcta(
? extends
U
,
? extends
V
) =
? extends
lub(
U
,
V
)
• lcta(
? extends
U
,
? super
V
) =
U
if
U
=
V
, otherwise
?
• lcta(
? super
U
,
? super
V
) =
? super
glb(
U
,
V
)
• lcta(
U
) =
?
if
U
's upper bound is
Object
, otherwise
? extends
lub(
U
,
Object
)
Finally, we define a bound for
T
j
based on on all the elements of the minimal erased
candidate set of its supertypes. If any of these elements are generic, we use the Can-
didateInvocation() function to recover the type argument information.
Define Candidate(
W
) = CandidateInvocation(
W
) if
W
is generic,
W
otherwise.
The inferred type for
T
j
, lub(
U
1
...
U
k
), is Candidate(
W
1
)
& ... &
Candidate(
W
r
), where
W
i
(1 ≤
i
≤
r
) are the elements of MEC.
It is possible that the process above yields an infinite type. This is permissible, and a Java
compiler must recognize such situations and represent them appropriately using cyclic data
structures.
The possibility of an infinite type stems from the recursive calls to lub(). Readers fa-
miliar with recursive types should note that an infinite type is not the same as a re-
cursive type.
