Regarding semantic version: it works in theory, but in practice applications often ends up relying on bugs, private APIs, or other kinds of non-public behavior.

Regarding semantic version: it works in theory, but in practice applications often ends up relying on bugs, private APIs, or other kinds of non-public behavior. For example the GNOME libraries have been following semantic versioning forever, yet sometimes an upgrade breaks something else because that something else was relying on a bug. In 2004 there was a famous case where upgrading your glib would break gnome-panel. This is of course not to say that semantic versioning is useless, but in practice you will still need some kind of version pinning system. As for "rvm and its ilk shouldn't even have to exist": you do realize that rvm and its ilk are not just to allow you to pin your software to a specific Ruby version, right? They're also there to allow you to easily upgrade to newer versions. Let's face it, compiling stuff by hand sucks, and your hair has turned white by the time the distro has caught up.