Confused by different behavior of assignments of Arrays and Numbers

[lmiq]

This is a common source of confusion for beginners (myself included). You can find related threads about it. One nice answer is this one:

Assignment and mutation

The simplest version of this I can come up with is this: Assignment changes which object a name refers to: x = ex causes the name x to refer to the value resulting from the evaluation of the expression ex. Assignment never changes the values of any objects. Mutation changes the value of an object: x[i] = ex and x.f = ex both mutate the object referred to by x changing a value at index or a property with a name, respectively. Mutation never changes what objects any names in any scope refer …