It is technically correct, but for example I was able to assign [a: ‘1’] to a Map<String, Object>, so for variable assignment it works, but not for plus.

 

In my second example I use Collections.emptyList(), which in Java exists expressly to avoid casts that are required when using Collections.EMPTY_LIST. So this is code that would work in Java exactly as-is but does not work in Groovy. It means that the ability to return template generic type seems not to exist in Groovy.

 

In both cases, I can use a cast to fix the issue, although in IntelliJ it’s annoying because it thinks you can’t cast a Map<String, Integer> to a Map<String, Object> (which would be true in Java code), although groovyc itself allows it. So then you have the awkward workaround of [b: (Object)2], which seems very anti-Groovy (especially given the very recent conversation on this list about removing unnecessary syntax around closures). In the second case, I can use Collections.<Integer>emptyList(), but in this case the Groovy code is more verbose than the Java code.

 

Jason

 

From: Cédric Champeau [mailto:cedric.champeau@gmail.com]
Sent: Wednesday, December 02, 2015 9:48 AM
To: users@groovy.apache.org
Subject: Re: CompileStatic and right-hand-side literals

 

I think that the type checker is technically correct here. The RHS is correctly inferred (it's a `Map<String, String>`). And since you are trying to assign it to `Map<String, Object>` it fails. It's a consequence of inference of literals (Java doesn't have such literals so no such issues). You have to separate declaration from assignment, or use a cast.

 

2015-12-02 15:44 GMT+01:00 Winnebeck, Jason <Jason.Winnebeck@windstream.com>:

Is there a way to avoid awkward typing issues with literals as in this case:

@CompileStatic
void f() {
  Map<String, Object> x = [a: '1']
  println x + [b: 2]
}

This results in the following errors in 2.4.5:

[Static type checking] - Incompatible generic argument types. Cannot assign java.util.LinkedHashMap <java.lang.String, java.lang.String> to: java.util.Map <String, Object>
 at line: 3, column: 27

[Static type checking] - Cannot call <K,V> java.util.LinkedHashMap <java.lang.String, java.lang.String>#plus(java.util.Map <java.lang.String, java.lang.String>) with arguments [java.util.LinkedHashMap <java.lang.String, java.lang.Integer>]
 at line: 4, column: 13

It seems that the static compiler has issues with inferring RHS types. I think it might be similar to this case I run into from time to time:

@CompileStatic
void g(List<Integer> items) {}

@CompileStatic
void h() {
  g(Collections.emptyList())
}

Results in:
[Static type checking] - Cannot call ConsoleScript6#g(java.util.List <java.lang.Integer>) with arguments [java.util.List <T extends java.lang.Object>]

Jason Winnebeck

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