groovy

POGOs no-arg constructor invocation and metaprogramming

Details

  • Type: Bug Bug
  • Status: Closed Closed
  • Priority: Major Major
  • Resolution: Fixed
  • Affects Version/s: 1.1-rc-3
  • Fix Version/s: 1.5
  • Component/s: class generator
  • Labels:
    None
  • Number of attachments :
    0

Description

The following code:

[code]
class DefaultNoArgCtor {
DefaultNoArgCtor(String s) {}

// DefaultNoArgCtor(int s) {} <== uncomment this line to get the BUG
}

def a = new DefaultNoArgCtor()
println a
[/code]

If you uncomment the 2nd constructor, then instead of getting an exception about not being able to find the ctor (or something similar)
what I am getting (trunk) is:

[trace]
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.codehaus.groovy.tools.GroovyStarter.rootLoader(GroovyStarter.java:101)
at org.codehaus.groovy.tools.GroovyStarter.main(GroovyStarter.java:130)
Caused by: java.lang.ClassCastException:
org.codehaus.groovy.reflection.CachedConstructor
at org.codehaus.groovy.runtime.metaclass.MethodSelectionException.appendMethods(MethodSelectionException.java:80)
at org.codehaus.groovy.runtime.metaclass.MethodSelectionException.getMessage(MethodSelectionException.java:59)
at java.lang.Throwable.getLocalizedMessage(Throwable.java:267)
at java.lang.Throwable.toString(Throwable.java:344)
at java.lang.String.valueOf(String.java:2615)
at java.lang.StringBuffer.append(StringBuffer.java:220)
at groovy.ui.GroovyMain.run(GroovyMain.java:319)
at groovy.ui.GroovyMain.process(GroovyMain.java:294)
at groovy.ui.GroovyMain.processArgs(GroovyMain.java:111)
at groovy.ui.GroovyMain.main(GroovyMain.java:92)
... 6 more
[/trace]

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Alexandru Popescu added a comment -

Comment history (from mailing list)

Playing with constructors and metaprogramming, I have found out that
all POGOs do have the default constructor, even if they do not declare
one.

[code]
class NoDefaultCtor {
def field

NoDefaultCtor(param)

{ field= param }

String toString() {
return "toS: $

{field.class.name}

"
}
}

a = new NoDefaultCtor("first")
println a // => toS: java.lang.String
b = new NoDefaultCtor() // I wouldn't expect this to work
// println b => NPE I do expect this
[/code]

Something that people should be aware of. The implication on
metaprogamming: you cannot add a no-arg constructor through the
metaclass, as there is already one in place.

Show
Alexandru Popescu added a comment - Comment history (from mailing list) Playing with constructors and metaprogramming, I have found out that all POGOs do have the default constructor, even if they do not declare one. [code] class NoDefaultCtor { def field NoDefaultCtor(param) { field= param } String toString() { return "toS: $ {field.class.name} " } } a = new NoDefaultCtor("first") println a // => toS: java.lang.String b = new NoDefaultCtor() // I wouldn't expect this to work // println b => NPE I do expect this [/code] Something that people should be aware of. The implication on metaprogamming: you cannot add a no-arg constructor through the metaclass, as there is already one in place.
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Alexandru Popescu added a comment -

However, the no-arg ctor is not in the bytecode, so I assume what Groovy does is to invoke the existing constructor with a null value.

Show
Alexandru Popescu added a comment - However, the no-arg ctor is not in the bytecode, so I assume what Groovy does is to invoke the existing constructor with a null value.
Alex Tkachman made changes -
Field Original Value New Value
Resolution Fixed [ 1 ]
Status Open [ 1 ] Resolved [ 5 ]
Guillaume Laforge made changes -
Status Resolved [ 5 ] Closed [ 6 ]

People

  • Assignee:
    Alex Tkachman
    Reporter:
    Alexandru Popescu
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Dates

  • Created:
    Updated:
    Resolved: