@Typed annotation stops Groovy code compiling

Question

Why does this Groovy code...

def mt(){
  def i= 0
  def c= {i++}
}

...compile, but this Groovy code...

@Typed def mt(){
  def i= 0
  def c= {i++}
}

...not compile with error...

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:  
C:\Users\gavin\Documents\Personal\Groovy\otherRun.groovy: 5: 
Cannot modify final field otherRun$mt$1.i @ line 5, column 11.  
 def c= {i++}
         ^

Answer 1

You can work around the restriction via the @Field annotation, like so:

@Typed def mt(){
    @Field def i = 0
    def c = {i++}
}

assert mt().call() == 0
assert mt().call() == 1