Migration From Classic to JSR syntax - Groovy

Here is a checklist of changes you'll need to make to a Groovy classic codebase to ensure compatibility with the new Groovy JSR syntax.

Safe navigation

In Classic Groovy we used to use this syntax

class Person = { String name }
y = null
println "${y->name}"    // -> was the optional gpath operator with Classic Groovy syntax

Instead of using the arrow operator for safe navigation to avoid NullPointerException, we're now using the ?. operator

Now in the JSR we use this syntax

class Person = { String name }
def y = null
println "${y?.name}"    // Now, ?. is the optional gpath operator the new Groovy JSR

Parameter separator in the closure syntax

This allows us to use one single token for the separator between the closure in Classic Groovy we used to use this syntax

cl = {a| ...}
cl = {|a| ...}

Now in the JSR we use this syntax

def cl = {a -> ...}

This allows us to use one single token for the separator between the closure parameters and the code in in the closure which works with arbitrarily complex parameter list expressions and default values. e.g.

def cl = {String x = "hey", int y = a|b -> println "Values are $x and $y"}
collection.each {int item -> println item}

Property keyword

property keyword has been replaced with an annotation

class Foo {
    property foo
}

class Foo {
    @Property foo
}

Introduction of the 'def' keyword

local variable declarations and fields currently need to be specified with 'def', a modifier, and/or a type. e.g.

def foo() {
  int x = 123
  y = 456 // classic
}

def foo() {
  int x = 123
  def y = 456 // JSR
}

class Foo {
    telson  // classic
    int sharna
}
class Foo {
    def telson  // JSR
    int sharna
}

(Syntactically, the new keyword 'def' acts for methods as a modifier like 'public'.)

For Scripts (as opposed to explicitely declared classes) the syntax is not changed, i.e. variable declarations without 'def' are still allowed, because those variables are automatically created in the script binding if they don't already exist.

Introduction of the 'as' keyword

We can change types of objects with using the 'as' keyword,
e.g.

def d0 = new Date(2005-1900, 5-1, 7)   // in classic Groovy or Java
println d0

def d1 = [2005-1900, 5-1, 8] as Date    // since jsr-01
println d1

Date d2 = [2005-1900, 5-1, 9] as Date   // since jsr-01
println d2

Date d3 = [2005-1900, 5-1, 10]          // since jsr-01
println d3

// def n0 = new int[] { 1, 3, 5, 6 }   // Not work. This style is not supported since groovy-1.0-jsr-01.

def n1 = [ 1, 3, 5, 7 ] as int[]
println n1.class
println n1.size()
println n1.length
println n1[0]
println n1[-1]

// int[] n2 = [ 2, 4, 6, 8,10 ] as int[]    // work
int[] n2 = [ 2, 4, 6, 8, 10 ]               // work
println n2.class
println n2.size()
println n2.length
println n2[0]
println n2[-1]

// String[] n3 = [ "a", "ab", "abc", "abcd", "abcde", "abcdef" ] as String[]    // work
String[] n3 = [ "a", "ab", "abc", "abcd", "abcde", "abcdef" ]                   // work
println n3.class
println n3.size()
println n3.length
println n3[0]
println n3[-1]

Default access level of class members

The default access level for members of Groovy classes has changed from "public" to "protected"

Classic Groovy

class Foo {
    readMe_a;
    readMe_b
}
xyz = new Foo(readMe_a:"Hello",readMe_b:"World")
println xyz.readMe_a
println xyz.readMe_b

Now in JSR Groovy

class Foo {
    public readMe_a;
    def readMe_b //def is now required because of the "def keyword" change mentioned earlier
}
xyz = new Foo(readMe_a:"Hello",readMe_b:"World")
println xyz.readMe_a
println xyz.readMe_b //errors in JSR Groovy

Array creation

no special array syntax. To make the language much cleaner, we now have a single syntax to work with lists and arrays in the JSR. Also note that we can now easily coerce from any collection or array to any array type

// classic
args = new String[] { "a", "b" }

// JSR
String[] args = ["a", "b"]
def x = [1, 2, 3] as int[]
long[] y = x

Be careful: we don't support native multi-dimensional array creation right now.

float and double notation

float and double literals cannot start with dot. So

x = .123 // classic
def x = 0.123 // JSR

This is to avoid ambiguity with things like ranges (1..2) and so forth

Explicit method pointer syntax

In classic Groovy you could access method pointers automatically if there was no java bean property of the given method name.

e.g.

// classic
methodPointer = System.out.println
methodPointer("Hello World")

This often caused confusion; as folks would use a property access to find something and get a method by accident (e.g. typo) and get confused. So now we make getting a method pointer explicit as follows

// JSR
def methodPointer = System.out.&println
methodPointer("Hello World")

def foo = ...
def p = foo.&bar

// lets call the bar method on the foo object
p(1, 2, 3)

No 'do ... while()' syntax as yet.

Due to ambiguity, we've not yet added support for do .. while to Groovy

'No Dumb Expression' rule

no dumb expression rule, so we will catch dumb expressions (where a carriage return has broken the script). e.g.
```
def foo() {
  def x = 1
  +5  // dumb expression!
  return 8
}
```

Markup and builders

markup / builders will change a little, but the classic syntax still applies. Not sure of the new syntax, but we'll have some kinda start/stop syntax to denote a markup block. Maybe a keyword, like

markup (builder) { 
  // same stuff as before goes here
}

// or something like this
builder.{
  // same stuff as before goes here
}

Strings and GStrings

single and double quote strings can only span one line; for multiple lines use triple quotes

heredocs removal - they are kinda ugly anyway . If you want to use them, just use treble quote instead

def foo = """
this 
is
a very
long 
string on many
lines
"""

escaping of $ inside GStrings must use \$

println 'amount is $100'
// same as
println "amount is \$100"

A new string definition is also supported which is escaping friendly, and thus particularly friendly for regex notation:

if ('abc' =~ /.../) {}
if ('abc' ==~ /.../) {}
'abc'.eachMatch(/.../) {}
['a','b','c'].grep(/a/)

switch('abc'){
       case ~/.../ : whatever
}

assert 'EUOUAE'.matches(/^[aeiou]*$/)
assert 'EUOUAE' ==~ /^[aeiou]*$/
assert 'football'.replaceAll(/foo/, "Bar") == 'Bartball'

Assertions

assert uses comma instead of colon to delimit the two parameter form of assertion statement

assert 0 <= value : "Must be non-negative"  // classic

assert 0 <= value , "Must be non-negative"  // JSR

return/break/continue semantics in closures

NOT YET IMPLEMENTED

return/break/continue to behave inside closures like these statements work in other blocks (such as the block on a for() or while() loop. More details here

Integer division

Previously, in Groovy Classic, we used the backward slash as the integer division operator. This operator being confusing with escaping sequences was removed. So instead of \ please use the intdiv() method.

int result = 5 \ 3 // classic

Becomes

int result = 5.intdiv(3) // JSR

JDK5 for loop not supported

Groovy already supports a fair number of looping mechanisms, and in Classic, both for (... : ...) and for (... in ...) were supported. For the moment, only the for (... in ...) notation is allowed.

for (e : myList) { } // not allowed anymore
for (Element e : myList) { } // not allowed anymore
for (e in myList) { } // JSR
for (Element e in myList) { } // JSR

Exclusive range

The operator for creating ranges with the upper bound excluded from the range has changed.

Instead of:

range = 0...10

The syntax is now:

def range = 0..<10