subroutines returning references to an array or hash and the role of + operator

Question

I found this feature in Perl and I'm not sure what it is.. Maybe someone can point me in the right direction.

Say I have a simple function like below:

sub get_arr {
    [1..9];
}

Now I can display this to the output with:

say "@{+get_arr}";

What is the + operator in this context?