I found an interesting issue when playing with metaclasses Apoliges for the large amount of

What I am trying to do in my code is this

Create an ArrayList of Person objects (call it people) then to demostrate the power of metaprogramming extend the people list wiih a few closures/methods that filter the list. My code looks like this

class Person {
  def name,age,sex,employed
}
def people = [
  new Person(name:"Person 1", age:67, sex:'male', employed:true),
  new Person(name:"Person 4", age:42, sex:'male', employed:true),
  new Person(name:"Person 8", age:21, sex:'male', employed:false)
]
/* sorting by age */
def byAge = {a,b ->
  a.age <=> b.age
}
/* ADD FILTERS DIRECTLY TO LIST */
people.class.metaClass.olderThanEighteen = {
  delegate.findAll{it.age > 18}
}
people.metaClass.males = {
  delegate.findAll{it.sex.equals('male')}
}
people.metaClass.inEmployment = {
  delegate.findAll{it.employed}
}
// more expressive??!
def filtered = people.males().olderThanEighteen().inEmployment().sort(byAge)
filtered.each {
  println "$it.name is an employed male older than 18"
}

When I run this code I get this error

groovy.lang.MissingPropertyException: No such property: olderThanEighteen for class: groovy.lang.MetaClassImpl
at Script0.run(Script0:14)

The quirk comes when I modify the "people.metaClass.olderThenEighteen" line to be "people.class.metaClass.olderThenEighteen" everything works from then onwards. Even the unmodifed lines "people.metaClass.males" and "people.metaClass.inEmployment". Can anyone explain why this is the case?

James.


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