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https://issues.apache.org/jira/browse/GROOVY-8660?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17364325#comment-17364325
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Eric Milles commented on GROOVY-8660:
-------------------------------------
I only found out about this a couple weeks ago. As best as I can gather, the
method selection (in MetaClassImpl) will translate "foo()" to "foo(null)" if
there is only one method "foo" for the receiver type and the method has one
non-primitive parameter. This extends to category methods, so a static
category method will apply to "foo()" if is has one self parameter and one
additional non-primitive parameter.
In your "Both" case, the one method criterion is not met. I'm not sure why
this exists and I think I have seen some discussion of removing it in MOP 2.0.
But I think that effort is largely stalled.
> Unexpected MethodSelectionException with implicit null argument
> ---------------------------------------------------------------
>
> Key: GROOVY-8660
> URL: https://issues.apache.org/jira/browse/GROOVY-8660
> Project: Groovy
> Issue Type: Bug
> Affects Versions: 3.0.0-alpha-2, 2.4.15, 2.5.0
> Reporter: Daniil Ovchinnikov
> Priority: Major
>
> {code:groovy}
> class OnlySingle {
> def foo(a) { "single param: $a" }
> }
> println new OnlySingle().foo()
> // as expected: 'single param: null'
> class OnlyVararg {
> def foo(a, ... b) { "vararg param: $a, $b" }
> }
> println new OnlyVararg().foo()
> // as expected: 'MME: No signature of method: OnlyVararg.foo() is applicable
> for argument types: () values: []'
> class Both {
> def foo(a) { "single param: $a" }
> def foo(a, ... b) { "vararg param: $a, $b" }
> }
> println new Both().foo()
> // unexpected:
> // MethodSelectionException: Could not find which method foo() to invoke from
> this list:
> // public java.lang.Object Both#foo(java.lang.Object)
> // public transient java.lang.Object Both#foo(java.lang.Object,
> [Ljava.lang.Object;)
> {code}
> If the exception is expected then {{OnlyVararg}} case should work too.
> If the exception is unexpected then {{Both#foo(Object)}} should be selected.
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