Groovy - ExpandoWithDelegate

ExpandoWithDelegate.groovy

class ExpandoWithDelegate {
   
   private delegate
   private Map<String, Closure> mockedMethods
   
   ExpandoWithDelegate(delegate) {
      this.delegate = delegate
      this.mockedMethods = [:]
   }
   
   def methodMissing(String name, args) {
     mockedMethods.containsKey(name) ?
       mockedMethods[name](*args) :
       delegate."$name"(*args) 
   }
   
   def propertyMissing(String name, value) { 
     if (value instanceof Closure) {
       value.delegate = delegate
       mockedMethods[name] = value 
     }
     else throw new MissingPropertyException(name, delegate.getClass())
   }
}
   
def var = new ExpandoWithDelegate('me molo')
assert var.size() == 7
var.size = { -> 42 }
assert var.size() == 42

assert var.concat(' mucho') == 'me molo mucho'
var.concat = { anotherString -> delegate.concat(anotherString).concat('!!!') }
assert var.concat(' mucho') == 'me molo mucho!!!'