TLDR On the distinction between `a = (a || b)` and `a || (a = b)`:

* There is no difference when `a` and `b` are local variables (unless `a` is undefined, but that's an edge case)

* The distinction manifests when `a=` is a method. (It could be a `[]=` or some attr_accessor). Then `a = (a || b)` always invokes `a=`, whereas `a || (a = b)` only invokes `a=` when `a` is falsey.

In essence however, `a ||= b` respects the intuitive definition that it sets `a` to `b` if and only if `a` is falsey.