Groovy spread operator map syntax with colon

I'm wondering why this syntax is not consistent for spreading lists and maps. For example in this code

def list =[1,2,3] def map =[a:1,b:2] println "${[*list]}" println "${[*:map]}" 

list is spreaded with single *, and map with *:

Is it connected to how spread operator internally works? Because didn't see any other usage for *map construct (like defining an empty map with [:] makes sense to distinguish it from list).

1 Answer

The spread operator (*) is used to extract entries from a collection and provide them as individual entries.

1. Spread list elements:

When used inside a list literal, the spread operator acts as if the spread element contents were inlined into the list:

def items = [4,5] def list = [1,2,3,*items,6] assert list == [1,2,3,4,5,6] 

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2. Spread map elements:

The spread map operator works in a similar manner as the spread list operator, but for maps. It allows you to inline the contents of a map into another map literal, like in the following example:

def m1 = [c:3, d:4] def map = [a:1, b:2, *:m1] assert map == [a:1, b:2, c:3, d:4]​ 

Source :