[GROOVY-8870] Spread-dot operator on list of lists

• Type: Documentation
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 3.0.0-alpha-4, 2.5.4
• Assignee: Paul King
• Reporter: Eric Milles
• Created: 06/Nov/18 22:14
• Updated: 13/Dec/18 10:04
• Resolved: 07/Nov/18 04:18

Description

I'm not sure if this is intended, but I ran into some nice/useful behavior of the spread-dot operator when applying to a list of lists. I was trying to use collectMany and found that I would need to do an inner collectMany or switch to inject. But it turns out spread-dot and flatten handled the situation very nicely.

Could you please add a note on this to the documentation (section 1.2.8 – other operators)? I don't think it is common knowledge that spread-dot does not always gather up results in a flat list.

class Foo {
  String thing
}
class Bar {
  List<Foo> foos
}
class Baz {
  List<Bar> bars
}

List<Foo> f = [new Foo(thing:'1'), new Foo(thing:'2')]
assert f*.thing == ['1','2']

List<Bar> b = [new Bar(foos:f), new Bar(foos:f)]
assert b*.foos*.thing == [['1','2'], ['1','2']]
assert b*.foos*.thing.flatten()​ == ['1','2','1','2']

// this was my use case:
List<Baz> z = [new Baz(bars:b), new Baz(bars:b)]
​assert z*.bars*.foos == [[f, f], [f, f]] // each f is a list of 2 Foos
assert z*.bars*.foos*.thing == [[['1','2'], ['1','2']], [['1','2'], ['1','2']]]
assert z*.bars*.foos*.thing.flatten()​ == ['1','2','1','2','1','2','1','2'] // for the win!

// in this case I could have also written it without the stars:
assert z.bars.foos.thing.flatten()​ == ['1','2','1','2','1','2','1','2']