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  1. Groovy
  2. GROOVY-8340

Static compilation error with a method parameter containing an array in a type parameter



    • Type: Bug
    • Status: Open
    • Priority: Major
    • Resolution: Unresolved
    • Affects Version/s: None
    • Fix Version/s: None
    • Component/s: Static compilation
    • Labels:


      A compilation error occurs when using static compilation and attempting to call a method with a parameterized argument that contains an array in the type parameter. The equivalent Java code has no issues.

      Here is a specific example:

      class ArrayGenericsIssue {
        static void main(String[] args) {
          Optional<Integer[]> o = Optional.of([1, 2, 3] as Integer[])
          Integer firstFromArray = getFirstFromArray(o) //This fails to compile
          println "First (array): $firstFromArray"
        static <E> E getFirstFromArray(Optional<E[]> optional) {
          return optional.get()[0]

      The error returned is:

      Error:(16, 30) Groovyc: [Static type checking] - Cannot call <E>ArrayGenericsIssue#getFirstFromArray(java.util.Optional <[Ljava.lang.Object;>) with arguments [java.util.Optional <[Ljava.lang.Integer;>

      The expected behavior is that this code would compile and run successfully with @CompileStatic enabled.

      Note that equivalent code with a non-array generic parameter works just fine:

        static void main(String[] args) {
          Optional<List<Integer>> o = Optional.of([1, 2, 3])
          Integer firstFromList = getFirstFromList(o) //This compiles just fine
          println "First (list): $firstFromList"
        static <E> E getFirstFromList(Optional<List<E>> optional) {
          return optional.get()[0]

      Additionally, there is no compilation issue if the value is cast to a raw type:

      Integer firstFromArray = getFirstFromArray((Optional) o2)

      For some context, I'm running into this issue when working with jOOQ, as some of its API involves working with array type parameters.




            • Assignee:
              mjjustin M. Justin
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              • Created: