In groovy when comparing this and a reference passed in a method: same instance, different metaclass -

in groovy 1.8.6, trying this:

class greeter {     def sayhello() {         this.metaclass.greeting = { system.out.println "hello!" }         greeting()     } }  new greeter().sayhello() 

this didn't work:

groovy.lang.missingpropertyexception: no such property: greeting class: groovy.lang.metaclassimpl 

after bit of trying, found passing reference self method did work. so, came this:

class greeter {     def sayhello(self) {         assert == self         // assert this.metaclass == self.metaclass          self.metaclass.greeting = { system.out.println "hello!" }         greeting()     } }  def greeter = new greeter() greeter.sayhello(greeter) 

the strangest thing assert == self passes, means same instance... right? default tostring seems confirm this.

on other hand, assert this.metaclass == self.metaclass fails:

assert this.metaclass == self.metaclass             |         |  |    |             |         |  |    org.codehaus.groovy.runtime.handlemetaclass@50c69133[groovy.lang.metaclassimpl@50c69133[class greeter]]             |         |  greeter@1c66d4b3             |         false             groovy.lang.metaclassimpl@50c69133[class greeter]  

why self.metaclass wrapped in handlemetaclass, while this.metaclass isn't? also, how can first example made work without passing in reference self?

you can implement methodmissing in class below answer last question:

class greeter {     def sayhello() {         //this.metaclass.greeting = { system.out.println "hello!" }         greeting()         goodnight()     }      def methodmissing(string name, args){         if(name == 'greeting'){             println "hello!"          } else             println "good night"     } }  new greeter().sayhello() 

also note == in groovy means equals() (that value comparison) if want compare identity is() can used like

a.is(b) //corresponds == in java == b //corresponds equals() in java 

update
can use metaclass below

greeter.metaclass.greeting = { println "hello"} def greet = new greeter()  //or //greet.metaclass.greeting = { println "hello"}  greet.sayhello()