Clint Eastwood has hit Cannes to promote his new film, The Exchange, starring Aneglina Jolie.The movie is based on a true story of a single mother in 1920s California whose son Walter vanishes.Months later police turn up with a boy they say is Walter - but his mother Christine senses immediately he is not her son.She battles to prove that the corrupt and incompetent Los Angeles Police Department will go to any lengths to make the case disappear.At a press conference the director, who will turn 78 next week, was asked whether he was planning a return to the role of Dirty Harry.Eastwood responded: "There are certain things you have to be realistic about. Dirty Harry would not be on a police department at my age."