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https://issues.apache.org/jira/browse/GROOVY-9075?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16907871#comment-16907871
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Daniel Sun commented on GROOVY-9075:
------------------------------------
You mean a better error message like the following one?
{code:java}
object[C2] is not an instance of declaring class[C1]
{code}
> The exception message should be more clear when a GroovyObject's metaClass is
> wrong
> -----------------------------------------------------------------------------------
>
> Key: GROOVY-9075
> URL: https://issues.apache.org/jira/browse/GROOVY-9075
> Project: Groovy
> Issue Type: Bug
> Components: groovy-runtime
> Affects Versions: 2.4.16, 3.0.0-alpha-4, 2.5.6
> Reporter: Xiaoguang Wang
> Priority: Major
>
> If a GroovyObject's metaClass is overwritten by mistake, the accesses to the
> instance may cause an exception with unclear message.
>
> We have met the problem too many times and have spent a lot of time on
> debugging (and teaching everyone never to use `BeanUtils.copyProperties`, etc)
>
> If there is a try-catch (or some other check) in the runtime code and report
> this problem more clearly, it will save everyone's time to debug. Or, is
> there any better solution to this problem, eg: check the class type in
> `MetaClassImpl.setProperty`, `DefaultGroovyMethods.setMetaClass` ?
>
> {code:java}
> import groovy.transform.CompileStatic
> //@CompileStatic
> class C1 {
> int x
> }
> //@CompileStatic
> class C2 {
> int x
> }
> //@CompileStatic
> class TestGroovy {
> static void main(String[] args) {
> def c1 = new C1()
> def c2 = new C2()
> c1.metaClass = c2.metaClass //eg:
> org.springframework.beans.BeanUtils.copyProperties
> // or c1.setMetaClass(c2.getMetaClass())
> c1.x += 1 // crash here with unclear exception, but c1.setX() works
> }
> }
> {code}
>
> {code:java}
> /*
> without @CompileStatic
> Exception in thread "main" java.lang.IllegalArgumentException: object is not
> an instance of declaring class
> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> at
> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
> at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
> at java.lang.reflect.Method.invoke(Method.java:498)
> at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
> at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
> at
> org.codehaus.groovy.runtime.metaclass.MethodMetaProperty$GetBeanMethodMetaProperty.getProperty(MethodMetaProperty.java:76)
> at
> org.codehaus.groovy.runtime.callsite.GetEffectivePogoPropertySite.getProperty(GetEffectivePogoPropertySite.java:85)
> at
> org.codehaus.groovy.runtime.callsite.AbstractCallSite.callGetProperty(AbstractCallSite.java:299)
> with @CompileStatic
> Exception in thread "main" java.lang.IllegalArgumentException: object is not
> an instance of declaring class
> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> at
> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
> at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
> at java.lang.reflect.Method.invoke(Method.java:498)
> at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
> at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
> at groovy.lang.MetaClassImpl.setProperty(MetaClassImpl.java:2726)
> at groovy.lang.MetaClassImpl.setProperty(MetaClassImpl.java:3785)
> at C1.setProperty(TestGroovy.groovy)
> at
> org.codehaus.groovy.runtime.InvokerHelper.setProperty(InvokerHelper.java:213)
> at
> org.codehaus.groovy.runtime.ScriptBytecodeAdapter.setProperty(ScriptBytecodeAdapter.java:497)
> */
> {code}
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