Is array_append O(n)?

Hi,

Does `array_append(arr, elt)` create a new array and copy everything? In other words, is it O(n) or O(1)? I’m trying to
useplpgsql and realizing I don’t really have my usual data structures for basic algorithms the way I’d normally write
them.I probably shouldn’t be treating arrays like Java ArrayList or C++ vector, where you can add/remove on the end
withlittle cost (O(1), almost.) 

Rob