Don't Use Implicit Return Types

JavaFX, like Scala, is a fully statically typed language. However, unlike Java, it allows you to omit type declarations in many places, since it can infer it. Coupled with the fact that you can use expressions as statements, and that the last expression in a function will be the return value, this lets you write really simple and clear code. def s = "Hello"; def len = s.length(); function product(a: Number, b: Number) { a * b } The function above shows an "Implicit Return Type": The compiler figures out the return type, which in this case will be a Number, and that is the signature computed for the function. Unfortunately, this can sometimes lead to trouble! Here's a real-world example: public function clearSelection() { selected = null; } This function clears the selection in a node. The intention of the developer was probably for this function to have a "void" return type. But that is not the return type! The last statement is an expression, an assignment, which has the type of the left hand side, which is actually a node. So the return type here is a Node! And it could easily have leaked an implementation class too. This may not seem like a big deal here, but what if a subclass wanted to override this function? It would try this: override function clearSelection() { super.clearSelection(); moreStuff(); } And this would fail compilation, with a surprising error messa...

Date: June, 30 2010
Url: http://blogs.sun.com/tor/entry/don_t_use_implicit_return

Others News