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Let's take the following simple expression:

((Double) null ?: 0).getClass()

Results:

  • Groovy 3: class java.lang.Double
  • Groovy 4: class java.lang.Integer

Does anyone know the reason for the different behaviour? I'd say Groovy 4 is correct since the casting is applied before the Elvis operator.

Checked, but couldn't find anything related in the Groovy 4 release notes: https://groovy-lang.org/releasenotes/groovy-4.0.html

ferenc.nagy
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1 Answers1

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From the docs the precedence of the ?: is much lower than typecast. Typecast (type) is level 1 precedence and the elvis operator ?: is 14 so it looks like Groovy 4 is doing the right thing.

https://groovy-lang.org/operators.html#_operator_precedence

and in Groovy 3 docs it is documented the same:

http://docs.groovy-lang.org/docs/groovy-3.0.18/html/documentation/#_operator_precedence

The only way I might explain it is simple bug in Groovy 3 that went unnoticed, or maybe a bug that was fixed in later versions of Groovy 3 depending on the version you're using to test it. It might be worth it to report it even though its fixed just so they could write a unit test to catch it in the future since it possibly went unnoticed.

chubbsondubs
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    Talked with some folks on the dev mailing list and the conclusion is: (1) The v4 behavior is correct (i.e. the type of the Elvis condition value should only be relevant when it is truthy). (2) A fix for a specific issue, fixed a broader set of things. Fragments of the behaviour are covered in various STC tests, but it does look like better test coverage for the dynamic cases is needed. See [Jira issue](https://issues.apache.org/jira/browse/GROOVY-8965) and [GitHub commit](https://github.com/apache/groovy/commit/d94ea203ea) – ferenc.nagy Aug 15 '23 at 11:41