It's not just the O(n), you must think of interface{} as a pair (concreteType, pointerToMutableData). It's a can of worms, allocating n*2 word-sized objects for

It's not just the O(n), you must think of interface{} as a pair (concreteType, pointerToMutableData). It's a can of worms, allocating n*2 word-sized objects for each rune is just the surface layer - strings in particular are immutable. I think Go does the right thing to make this allocation and assignment explicit, you may be a little less surprised with how the program actually behaves. https://go.dev/play/p/PzuBpM66VX2 https://go.dev/play/p/PzuBpM66VX2