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https://issues.apache.org/jira/browse/GROOVY-8660?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17364269#comment-17364269
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Daniil Ovchinnikov edited comment on GROOVY-8660 at 6/16/21, 12:07 PM:
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This should be documented somewhere. Last time I've checked, there was
something like: "if a method can be called with a single null argument, then
the argument can be omitted", there was no mention that the method must not
have overloads or varargs.
If {{new OnlyVararg().foo()}} fails
=> {{Both#foo(Object, [LObject; )}} must be inapplicable
=> method selection in {{new Both().foo()}} should try only
{{Both#foo(Object)}} against {{null}} argument
=> {{Both#foo(Object)}} should be selected.
Now let's reverse the above.
If {{Both#foo(Object)}} is not selected
=> method selection in {{new Both().foo()}} actually sees both methods as
applicable before trying them with null argument
=> {{Both#foo(Object, [LObject; )}} was applicable
=> {{new OnlyVararg().foo()}} must not fail.
I'm having trouble understanding `org.codehaus.groovy.*` code. Can you describe
me the algorithm in human words, please?
was (Author: daniilo):
This should be documented somewhere. Last time I've checked, there was
something like: "if a method can be called with a single null argument, then
the argument can be omitted", there was no mention that the method must not
have overloads or varargs.
If {{new OnlyVararg().foo()}} fails
=> {{Both#foo(Object, [LObject;)}} must be inapplicable
=> method selection in {{new Both().foo()}} should try only
{{Both#foo(Object)}} against {{null}} argument
=> {{Both#foo(Object)}} should be selected.
Now let's reverse the above.
If {{Both#foo(Object)}} is not selected
=> method selection in {{new Both().foo()}} actually sees both methods as
applicable before trying them with null argument
=> {{Both#foo(Object, [LObject;)}} was applicable
=> {{new OnlyVararg().foo()}} must not fail.
I'm having trouble understanding `org.codehaus.groovy.*` code. Can you describe
me the algorithm in human words, please?
> 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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