[
https://issues.apache.org/jira/browse/GROOVY-12754?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Scott Murphy Heiberg updated GROOVY-12754:
------------------------------------------
Description:
Static type checking rejects a call that passes an upper-bounded wildcard, such
as {{List<? extends Integer>}}, to a generic method whose type parameter is
bounded by a supertype of the wildcard's bound. It accepts the call when the
wildcard's bound is wider than the type parameter's. javac does the opposite in
both cases.
{code:groovy}
@groovy.transform.CompileStatic
class C {
static <T extends Number> T first(List<T> list) { list.get(0) }
static <T extends CharSequence> int len(Class<T> type) { 0 }
static <T extends Integer> T narrow(List<T> list) { list.get(0) }
static Object a(List<? extends Integer> ints) { first(ints) } // rejected,
javac accepts
static int b(Class<? extends String> type) { len(type) } // rejected,
javac accepts
static Object c(List<? extends Number> nums) { narrow(nums) } // accepted,
javac rejects
}
{code}
{noformat}
[Static type checking] - Cannot call <T extends java.lang.Number>
C#first(java.util.List<T>) with arguments [java.util.List<? extends
java.lang.Integer>]
[Static type checking] - Cannot call <T extends java.lang.CharSequence>
C#len(java.lang.Class<T>) with arguments [java.lang.Class<? extends
java.lang.String>]
{noformat}
The capture of {{? extends B}} is a subtype of {{B}} (JLS 5.1.10), so it is
within the bound of {{T}} exactly when {{B}} is. javac reports "inference
variable T has incompatible bounds" for {{c}}. Groovy compiles {{c}}, and
{{c([1.5d])}} returns {{1}}.
{{StaticTypeCheckingSupport#compatibleConnection}} tests a wildcard witness
with {{connection.isCompatibleWith(bound)}}, which asks whether the type
parameter's bound fits within {{? extends B}}. For a type argument {{B}}, it
tests {{? super B}} against the bound. An upper-bounded wildcard should take
the same test.
PR: https://github.com/apache/groovy/pull/3285
was:
Static type checking rejects a call that passes an upper-bounded wildcard, such
as {{List<? extends Integer>}}, to a generic method whose type parameter is
bounded by a supertype of the wildcard's bound. It accepts the call when the
wildcard's bound is wider than the type parameter's. javac does the opposite in
both cases.
{code:groovy}
@groovy.transform.CompileStatic
class C {
static <T extends Number> T first(List<T> list) { list.get(0) }
static <T extends CharSequence> int len(Class<T> type) { 0 }
static <T extends Integer> T narrow(List<T> list) { list.get(0) }
static Object a(List<? extends Integer> ints) { first(ints) } // rejected,
javac accepts
static int b(Class<? extends String> type) { len(type) } // rejected,
javac accepts
static Object c(List<? extends Number> nums) { narrow(nums) } // accepted,
javac rejects
}
{code}
{noformat}
[Static type checking] - Cannot call <T extends java.lang.Number>
C#first(java.util.List<T>) with arguments [java.util.List<? extends
java.lang.Integer>]
[Static type checking] - Cannot call <T extends java.lang.CharSequence>
C#len(java.lang.Class<T>) with arguments [java.lang.Class<? extends
java.lang.String>]
{noformat}
The capture of {{? extends B}} is a subtype of {{B}} (JLS 5.1.10), so it is
within the bound of {{T}} exactly when {{B}} is. javac reports "inference
variable T has incompatible bounds" for {{c}}. Groovy compiles {{c}}, and
{{c([1.5d])}} returns {{1}}.
{{StaticTypeCheckingSupport#compatibleConnection}} tests a wildcard witness
with {{connection.isCompatibleWith(bound)}}, which asks whether the type
parameter's bound fits within {{? extends B}}. For a type argument {{B}}, it
tests {{? super B}} against the bound. An upper-bounded wildcard should take
the same test.
> STC: an upper-bounded wildcard argument is checked against a type parameter's
> bound the wrong way round
> -------------------------------------------------------------------------------------------------------
>
> Key: GROOVY-12754
> URL: https://issues.apache.org/jira/browse/GROOVY-12754
> Project: Groovy
> Issue Type: Bug
> Components: Static Type Checker
> Affects Versions: 6.0.0
> Reporter: Scott Murphy Heiberg
> Priority: Major
>
> Static type checking rejects a call that passes an upper-bounded wildcard,
> such as {{List<? extends Integer>}}, to a generic method whose type parameter
> is bounded by a supertype of the wildcard's bound. It accepts the call when
> the wildcard's bound is wider than the type parameter's. javac does the
> opposite in both cases.
> {code:groovy}
> @groovy.transform.CompileStatic
> class C {
> static <T extends Number> T first(List<T> list) { list.get(0) }
> static <T extends CharSequence> int len(Class<T> type) { 0 }
> static <T extends Integer> T narrow(List<T> list) { list.get(0) }
> static Object a(List<? extends Integer> ints) { first(ints) } //
> rejected, javac accepts
> static int b(Class<? extends String> type) { len(type) } //
> rejected, javac accepts
> static Object c(List<? extends Number> nums) { narrow(nums) } //
> accepted, javac rejects
> }
> {code}
> {noformat}
> [Static type checking] - Cannot call <T extends java.lang.Number>
> C#first(java.util.List<T>) with arguments [java.util.List<? extends
> java.lang.Integer>]
> [Static type checking] - Cannot call <T extends java.lang.CharSequence>
> C#len(java.lang.Class<T>) with arguments [java.lang.Class<? extends
> java.lang.String>]
> {noformat}
> The capture of {{? extends B}} is a subtype of {{B}} (JLS 5.1.10), so it is
> within the bound of {{T}} exactly when {{B}} is. javac reports "inference
> variable T has incompatible bounds" for {{c}}. Groovy compiles {{c}}, and
> {{c([1.5d])}} returns {{1}}.
> {{StaticTypeCheckingSupport#compatibleConnection}} tests a wildcard witness
> with {{connection.isCompatibleWith(bound)}}, which asks whether the type
> parameter's bound fits within {{? extends B}}. For a type argument {{B}}, it
> tests {{? super B}} against the bound. An upper-bounded wildcard should take
> the same test.
> PR: https://github.com/apache/groovy/pull/3285
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