Groovy：封闭中的冒号？

Question

I am trying to make my own Dsl and was playing around with different styles of closures in groovy. I've stumbled upon follwing snippet:

myClosure {
  testProperty: "hello!"
}

But can't figure out if this a valid code and how can I access then this testProperty . Is it valid? How can I read "hello!" value?

Answer 1

For now, lets put aside closures, consider the following code:

def f1() {
  testProperty : 5  
}
def f2() {
  testProperty : "Hello"
}
println f1()
println f1().getClass()
println f2()
println f2().getClass()

This compiles (therefor the syntax is valid) and prints:

5
class java.lang.Integer
Hello
class java.lang.String

So what you see here is just a labeled statement (groovy supports labels see here )

And bottom line the code of f1 (just like f2) is:

def f1() {
  return 5 // and return is optional, so we don't have to write it
}

With closures its just the same from this standpoint:

​def method(Closure c) {
  def result = c.call()
  println result
  println result.getClass()
}

method {
   test : "hello"
}

This prints

hello
class java.lang.String

as expected

Answer 2

Usually in DSL you have either this:

mySomething {
  a = 42
  b = 84
}

which corresponds to property setting

or this:

mySomething( a:42, b:84 ){
   somethingElse{}
}

which is a method call with Map-literal.

The code you shown is not used as @mark-bramnik explained.