Appending elements to a groovy list brings a hidden problem inside due to overriden operators. output+=item output.add(item) Is not always the same.

groovy-append2list-warn

def input=[1,[2,3],4]
def output=[]

//Warning!! Potential error
input.each{
   output+=it
}
println output       //=>[1,2,3,4]!!!
println output.size()//=>4

//Right way
output=[]
input.each{
   output.add(it)
}
println output       //=>[1,[2,3],4]!!!
println output.size()//=>3