#typechecked

Here's a simple example. What will this code print?

class Categorizer { void accept(String s) { println "String: '$s'" } void accept(Number n) { println "Number: $n" } void accept(Object o) { println "Object: $o" } void accept(Object... objects) { objects.each { accept(it) } } } new Categorizer().accept( "a", "${'b'}", 1, true, ["c", "d", 2] as Object[] )

This is straight up dynamic Groovy so we get this:

String: 'a' String: 'b' Number: 1 Object: true String: 'c' String: 'd' Number: 2

Dynamically compiled Groovy uses runtime method dispatch meaning that the version of Categorizer.accept to use for the statement accept(it) is determined at runtime based on the type of it.

What happens to that output if we add @CompileStatic to the Categorizer class? The output changes to this:

Object: a Object: b Object: 1 Object: true Object: [c, d, 2]

Now the statement accept(it) is bound at compile time and there is no type information about it. The compiler's only choice is to bind to accept(Object).

This is completely logical when you understand what the compiler is doing but it's behavior that annoyed me back when I was using Java full time and I much prefer Groovy's runtime dispatch.