Bugzilla – Full Text Bug Listing
| Summary: | [1.8][inference] Receiving The target type of this expression must be a functional interface | ||||||
|---|---|---|---|---|---|---|---|
| Product: | [Eclipse Project] JDT | Reporter: | kanagamahendran velusamy <kvelusamy> | ||||
| Component: | Core | Assignee: | Stephan Herrmann <stephan.herrmann> | ||||
| Status: | VERIFIED FIXED | QA Contact: | |||||
| Severity: | major | ||||||
| Priority: | P3 | CC: | jarthana, kvelusamy, manoj.palat, stephan.herrmann | ||||
| Version: | 4.10 | ||||||
| Target Milestone: | 4.12 M3 | ||||||
| Hardware: | PC | ||||||
| OS: | Windows 10 | ||||||
| See Also: |
https://git.eclipse.org/c/jdt/eclipse.jdt.core.git/commit/?h=R4_5_maintenance&id=dba3d88819f31e52c7b1709da4ad2221836bbba2 https://bugs.eclipse.org/bugs/show_bug.cgi?id=463728 https://git.eclipse.org/r/142384 https://git.eclipse.org/c/jdt/eclipse.jdt.core.git/commit/?id=5147f38abb400d33a4aa49de5af5318835c60b88 |
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This error is happening in eclipse 2018-12 latest public stable eclipse version ,however this is happening in Luna version. Thanks I can reproduce. The program was accepted up until 4.5, the change is caused by the fix for bug 463728 The corresponding commit only ensures we are always looking into result expressions of a lambda, even if the resultType is not yet known. At first glance this fix looks innocent. I could only vaguely imagine, that it causes some premature type information to become sticky and prevent the correct typing later. Until we figure out if this indeed is a regression or in line with JLS (which can take a while since these are complex issues), the following workaround can be used: return this.<FIReturnType>method1(()-> { ... the workaround
return this.<FIReturnType>method1(()-> { ...
or
return (FIReturnType)method1(()-> { ...
are working without error in eclipse
The java compiler ,compiles for
return method1(()->{...
it is good to have same feature in eclipse as well.
Thank you for your time!
I had a wrong copy paste in the above comment...
The workaround
return this.<FIReturnType>method1(()-> { ...
or
return method1(()-> {
return (FIReturnType) () ->{ ...
are working without error in eclipse
The java compiler ,compiles for
return method1(()->{...
it is good to have same feature in eclipse as well.
Thank you for your time!
New Gerrit change created: https://git.eclipse.org/r/142384 (In reply to Eclipse Genie from comment #5) > New Gerrit change created: https://git.eclipse.org/r/142384 I made an interesting find: Inference is rejecting the inner lambda because at this point its target type is an inference variable. JLS §18.2.1. says: "A constraint formula of the form ‹LambdaExpression → T›, where T mentions at least one inference variable, is reduced as follows: * If T is not a functional interface type (§9.8), the constraint reduces to false." An interface variable is not a functional interface type, hence ecj rejecting the program looks correct per JLS. Apparently, s.t. is missing in JLS to prevent this undesirable effect, and interestingly, a first test run doesn't complain if I invent another rule: * If T is an inference variable, the constraint reduces to true (delegating the details to inner inference) Let's see what full test run says. Gerrit change https://git.eclipse.org/r/142384 was merged to [master]. Commit: http://git.eclipse.org/c/jdt/eclipse.jdt.core.git/commit/?id=5147f38abb400d33a4aa49de5af5318835c60b88 (In reply to Eclipse Genie from comment #7) > Gerrit change https://git.eclipse.org/r/142384 was merged to [master]. > Commit: > http://git.eclipse.org/c/jdt/eclipse.jdt.core.git/commit/ > ?id=5147f38abb400d33a4aa49de5af5318835c60b88 Released for 4.12 M3 Verified for Eclipse Version: 2019-06 (4.12) Build id: I20190520-0600 |
Created attachment 277867 [details] the java class Please see the attached java class. Java compiler is able to compile correctly where as eclipse is showing error (version 4.4 with Luna - its working fine) public class Main { public static void main(String[] args) { System.out.println(new Main().getDetailCellCssFactory().getReturn()); } public FIReturnType getDetailCellCssFactory() { return method1(()-> { return () ->{ return "something"; }; }); } public <X> X method1(FIWithGenerics<X> init) { return init.init(); } } interface FIReturnType { String getReturn(); } interface FIWithGenerics<X> { X init(); } --------------------------------------------- it is giving these two errors The target type of this expression must be a functional interface The method method1(FIWithGenerics<X>) in the type Main is not applicable for the arguments (() -> {})