Daniel Sun created GROOVY-12319:
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Summary: Java compatibility: remaining generic type syntax
Key: GROOVY-12319
URL: https://issues.apache.org/jira/browse/GROOVY-12319
Project: Groovy
Issue Type: Improvement
Reporter: Daniel Sun
Groovy already accepts most Java generics. Three Java forms still fail — two in
the parser, one in {{GenericsVisitor}}. Each has a local workaround. Method
type arguments such as {{Helper.<String>identity(x\)}} already work and are not
part of this request.
h3. 1. Diamond {{<>}} on an anonymous class
Java 9+ (JEP 213) allows:
{code:java}
Processor<String> p = new Processor<>() {
public String process(String val) { return val; }
};
{code}
Groovy rejects this with {{Cannot use diamond <> with anonymous inner
classes}}. Writing new Processor<String>() \{ ... \} compiles.
GROOVY-6730 and GROOVY-7159 were false-positive STC errors when diamond was
_not_ used; they did not add this form.
h3. 2. Qualified parameterized inner types ("rare" types)
Java allows an inner type to keep the outer's type arguments:
{code:java}
class Outer<T> {
class Inner<U> {}
}
Outer<String>.Inner<Integer> x;
{code}
Groovy fails to parse {{Outer<String>.Inner}} ({{Unexpected input}}). A factory
that returns {{Inner}} without naming {{Outer<T>.Inner}} is a workaround. The
same qualification appears in {{o.new Inner<Integer>(42)}}.
h3. 3. Explicit type arguments on constructors, {{this()}} and {{super()}}
Java allows:
{code:java}
class Box {
<T> Box(T t) {}
}
new <String>Box("x");
{code}
and, on generic constructors, {{<T>this()}}, {{<T>super()}},
{{recv.<T>super()}}, and {{outer.new <T>Inner(...)}}.
Groovy fails at {{new <}} with {{Unexpected input: '<'}}. Inference ({{new
Box("x")}}) is the workaround.
Constructor type arguments are already tracked by GROOVY-10501. The {{this()}}
/ {{super()}} / inner-{{new}} forms are the same JLS production (JLS 15.9) and
should be handled together.
h3. Related
* GROOVY-10501 — constructor type arguments (open)
* GROOVY-6730, GROOVY-7159 — diamond + anonymous class, STC false positives
(fixed)
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