[Java] Annotation Type Newify

Annotation that supports writing constructor call expressions without the 'new' keyword. Instead they can be written "Ruby-style" as a method call to a 'new' method or "Python-style" by just omitting the 'new' keyword.

It allows you to write code snippets like this ("Python-style"):

 @Newify([Tree,Leaf]) class MyTreeProcessor {
     def myTree = Tree(Tree(Leaf("A"), Leaf("B")), Leaf("C"))
     def process() { ... }
 }
 

or this ("Ruby-style"):

 @Newify class MyTreeProcessor {
     def myTree = Tree.new(Tree.new(Leaf.new("A"), Leaf.new("B")), Leaf.new("C"))
     def process() { ... }
 }
 

After the AST transformation, the following code is passed on for further compilation:

 class MyTreeProcessor {
     def myTree = new Tree(new Tree(new Leaf("A"), new Leaf("B")), new Leaf("C"))
     def process() { ... }
 }
 

The annotation can be used on a whole class as shown above or selectively on a particular method, constructor or field.

The "Ruby-style" new conversions occur automatically unless the 'auto=false' flag is given when using the annotation. You might do this if you create a new method using meta programming.

The "Python-style" conversions require you to specify each class on which you want them to apply. The transformation then works by matching the basename of the provided classes to any similarly named instance method calls not specifically bound to an object, i.e. associated with the 'this' object. In other words Leaf("A") would be transformed to new Leaf("A") but x.Leaf("A") would not be touched.

An example showing how to use the annotation at different levels:

 @Newify(auto=false, value=Foo)
 class Main {
     @Newify // turn auto on for field
     def field1 = java.math.BigInteger.new(42)
     def field2, field3, field4

     @Newify(Bar)
     def process() {
         field2 = Bar("my bar")
     }

     @Newify(Baz)
     Main() {
         field3 = Foo("my foo")
         field4 = Baz("my baz")
     }
 }
 

The annotation is intended to be used sparingly; perhaps in DSL scenarios or when using deeply nested structural types. In particular, there is no support for using the facility with two similarly named classes from different packages at the same time. Though it is OK to have different packages in different contexts. Also, there is no support for turning "Ruby-style" conversions off at the method, constructor or field level if already turned on at the class level.

Authors:

Paul King