How Does the any Method Work in Groovy?

Question

I came across this bit of code:

n = args[0] as Long
[*n..1, n].any{ println ' '*it + '*'*(n - ~n - it*2) }

It's used for printing a tree form of structure. Like this:

    *
   ***
  *****
 *******
    *

(for n=4)

1. How does the code [*n..1,n] produce [4, 3, 2, 1, 4]?

2. How does any method works here? The Doc doesn't help me much. What is a predictive that can be passed to any(as mentioned in Doc's)?

Whats the use of any and how its handled in this case?

Burtis

@DownVoter : why a downvote? any wrong in this question ;) ? – Baeza

Answer 1

Q1a: * "unpacks" an array. .. creates a range. [] creates a collection.
Q1b: *n..1 unpacks [4,3,2,1] into its individual parts.
Q1c: [4,3,2,1,n] == [4,3,2,1,4]

Q2: I don't know why any was used here; each works just as well, and makes more sense in context. any does loop over the connection, so the println side-effect functions as intended.

Normally any would be used to determine if any collection elements met a criteria, for example:

[*n..1,n].any { it > 10 } // Returns false, no elements are > 10
[*n..1,n].any { it == 3 } // Returns true, because at least one element is 3

The last statement of the closure is used to determine if each item meets the criteria. println returns null, so any will return false. The value is unused and discarded.

The only reason I can think of that someone might have used any is to avoid seeing the return value of each in the console. each returns the original collection.

Sociality

Other reason to have used .any is to use the least number of characters in Code Golf Competition How to print out a Christmas tree of height N – Distinctly

Answer 2

1) n..1 is called a range literal, it creates a groovy.lang.Range object that decrements by 1 from n to 1. This is then merged into the surrounding list context using the "Spread operator (*)"

2) the any method is defined in DefaultGroovyMethods and it is a predicate function that returns true if an element in a collection satisfies the supplied predicate closure. In this example, the code doesn't check the return value, so original other could have produced the same output using an each call instead.

Canard