CODEWITHSUNDEEP
groovymetaclass
gt124
gt124

Reputation: 1258

groovy invokeMethod add method to metaclass needs if statement?

I've noticed some strange behavior with the Groovy MetaClass and I'm wondering if anyone can give me a clue to what's happening here.

This works fine:

@Override
Object invokeMethod(String name, Object args) {
    if(true) {
        println("Should only see this once")
        def impl = { Object theArgs -> println("Firing WeirdAction") }
        getMetaClass()."$name" = impl
        return impl(args)
    }
}

However if I take off the if statement it throws a MissingPropertyException:

@Override
Object invokeMethod(String name, Object args) {
    println("Should only see this once")
    def impl = { Object theArgs -> println("Firing WeirdAction") }
    getMetaClass()."$name" = impl
    return impl(args)
}

Here's my class instantiation and call, the class is empty except for the above method definition.

IfTester sut = new IfTester()
sut.WeirdAction()

Anyone have an idea what I'm misunderstanding here?

Upvotes: 4

Views: 406

Answers (1)

Michael Easter
Michael Easter

Reputation: 24468

Using Groovy 2.4.5, the issue appears to be related to getMetaClass() versus IfTester.getMetaClass(). Consider:

class IfTester {

    @Override
    Object invokeMethod(String name, Object args) {
        if (true) {
        println "Should only see this once"
        def impl = { def theArgs -> println "Firing WeirdAction" }
        def mc1 = getMetaClass()
        println "mc1: " + mc1
        println "----"
        def mc2 = IfTester.getMetaClass()
        println "mc2: " + mc2
        IfTester.getMetaClass()."$name" = impl
        return impl(args)
        }
    }
} 

IfTester sut = new IfTester()
sut.WeirdAction()

With the if(true), then mc1 and mc2 are identical, and both work. Without the if, mc1 is different and using that style causes the error.

I don't know the root cause, nor if it is a bug. Somehow, it seems that there is a scoping issue or that the sense of this is different in that context.

Upvotes: 1

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