Property reference operator

Groovy 1.0 already has the method reference operator:

class X {
   def doSomething() { println "hello" }
}

def obj = new X()

def methRef = obj.&doSomething
methRef()

class X {
   def someValue
}

def obj = new X()

def propRef = obj.&someValue // same syntax, but runtime knows it is a property
println propRef.value
propRef.value = 999
println propRef.name // outputs "someValue"
assert propRef.object == obj

// static property equivalent
def propRef = X.&someValue
// Now you need to pass in an instance
propRef.setValue( new X(), 123)

class AddressBookEntry

Property access in groovy is not problematic using GPath or subscript operator anyway, so this may not seem so useful. However if we could get some compile-time checking of the validity of the property that would be a nice win. Perhaps combining with the @ operator:

class AddressBookEntry {
     Address home
     Address work
     String name

     static embedded = [ &@home, &@work ]
}

named parameters everywhere

the proposal is that for functions defined inside groovy or where the debug information is availlable can be called with the map construct to provide named parameter calling everywhere 

void helloworld(name, title) {println "hello $title $name"}
can be called as
helloworld( title:"mr.", name:"koen" )

smarter nulls

def hello = "hello"
def test = null
println "$hello$test"

variable constraints

Keep dynamic typing while adding real type safety with constraints on variables that all must be true.  Though not all these constraints are actually useful they are there for illustrative purposes.

percent : as Integer, >= 0, <= 100
total : != 0
...
percent = num/total

Embedded XML

The programming language Scala has built-in support for XML. You can create something like this (taken from the Scala overview document):

val labPhoneBook =
    <phonebook>
        <descr>Phone numbers of<b>XML</b> hackers.</descr>
        <entry>
            <name>Burak</name>
            <phone where="work"> +41 21 693 68 67 </phone>
            <phone where="mobile"> +41 78 601 54 36 </phone>
        </entry>
    </phonebook>;

 Decoupling of static and instance methods

Also taken from the Scala programming language. It doesn't have static methods. All the static methods should be placed in a singleton. Static members are not a part of instance variables, so you shouldn't have to declare them in the same class.

 New way of declaring Expando

Could be just like in annonymous types in C#. For example:

def foo = new (prop:"value")
foo.bar = "bar"

First Class Support for User-Defined Boolean Types

There is already quite good support for user-defined numeric data (e.g. classes that act like numeric data in expressions) using the current support for operator overloading.  But if one needs to define a class that operates in expressions like a Boolean, it can't be done.  The following changes would make this possible and these seem consistent with the overall idea and design of Groovy:

1. Enable operator overloading for logical AND, logical OR, logical NOT. For logical AND and logical OR, the deferred evaluation of the right operand can be maintained by passing a Closure to the method.  The signatures might be something like this:

   Boolean land(Closure)                                  Boolean lor(Closure)

2. Enable assignment operator overloading.  This is needed to allow a semantic like

   MyBooleanClass bool = true

   Note that overriding the assignment operator makes it significantly easier to replace numeric types too since one can handle cases like

   MyNumericClass num = 10

   which is not possible today.

3. Today due to "Groovy Truth" processing, any non-null object reference (that is not a Boolean) will evaluate to true.  To enable user-defined Boolean type data, Groovy Truth would need to be modified to optionally "unbox" a non-null object reference into a Boolean value if it has a booleanValue() method.  This would allow one to do something like this

   MyBooleanType bool = something(); if bool || somethingElse() { ... }

   In such a case, the bool instance can be either false or true and can be directly used for control flow and other operations that normally expect a Boolean.
   
   With these changes, user-defined boolean replacement classes would get first-class support in the language.
   
   
   
   

 Smalltalk-like syntax for methods

 I've seen that in Groovy 1.5 it was possible to avoid using parenthesis when calling a method. It was made to simplify the reading in a more natural way...  

Nevertheless I'm not sure that the goal is  today reached... The groovy syntax was primarly  settled to make the step from Java easier for java coders...Along the versions, some syntactic sugar was added to fulfill new needs...to reach the point where going from jav to groovy is not so straightforward... Personnaly it is not an issue, but I would like to point out that if we differ more and more from java, why not adopting a syntax which is more accurate and simpler?

Personnaly, I find the Smalltalk syntax simpler and more elegant... I think that we could add some syntactic "tournures" of Smalltalk in Groovy 2.0, especially for defining new methods....

definition example : 

def print: anObject on: aStream {
....
}

or

def print: Customer aCustomer on: FileStream aStream {
...
}

 or better

def print: aCustomer as Customer  on: aStream as FileStream {
...
}

use example :

def aCustomer = new Customer();
WriteStream aStream = new FileStream();
print:aCustomer on: aStream ;