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https://issues.apache.org/jira/browse/GROOVY-8310?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16971093#comment-16971093
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Eric Milles commented on GROOVY-8310:
-------------------------------------
Because covariance does not extend to the generics, {{Closure<Collection>}} and
{{Closure<List>}} are not the same types. If you change the signature of bar
to {{Closure<? extends Collection<Integer>}} or cast the list expression to
{{Collection<Integer>}}, there are no errors.
So if the difference between the return types is fixed, there will be an error
for "def bar(...)" and "public <T> T bar(...)".
> Strange @CompileStatic check in Closure
> ----------------------------------------
>
> Key: GROOVY-8310
> URL: https://issues.apache.org/jira/browse/GROOVY-8310
> Project: Groovy
> Issue Type: Bug
> Components: Static compilation, Static Type Checker
> Reporter: Alexey Afanasiev
> Priority: Major
>
> This code compiles normal:
> {code}
> @CompileStatic
> class B {
> public <T> T bar(Closure<Collection<Integer>> a) {
> return null
> }
> def use() {
> bar {
> [1]
> }
> }
> }
> {code}
> Switching return type cause error in code:
> {code}
> import groovy.transform.CompileStatic
> @CompileStatic
> class B {
> public def bar(Closure<Collection<Integer>> a) {
> return null
> }
> def use() {
> bar { // Error:(21, 9) Groovyc: [Static type checking] - Cannot find
> matching method pack.B#bar(groovy.lang.Closure <java.util.List>).
> [1]
> }
> }
> }
> {code}
> I believe first example should have error too. But probably after fixing in
> that way following code will be broken:
> {code}
> def foo() {
> def nums = [1]
> def res = nums.collectMany { [it] }
> }
> {code}
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