Retractible Swords

I've always liked strange fictional weapons. Recently, I've been noticing myself really liking retractible swords and wishing I could get one somewhere. There are collapsible ceremonial swords, but those aren't actually useable. This recent interest of mine is probably due to spending large amounts of Dishonored. There are crossbow pistols on the market, which I do like, but Corvo's coolest gadget by far is his sword. It extends out if the handle like a lightsaber, only it's made of metal. It even has a slight curve to it, which makes it more difficult to make in real life, but much cooler looking, plus it has more slicing power that way. There are other examples of cool retractible swords, but besides the one briefly wielded by Sulu in the newest Star Trek movie ( the next one looks pretty great by the way), I can't think of any more right now. It's a fairly simple concept, but as radical as Star Wars was when it came out, now there are so many franchises with characters who wield retracting energy blades that I find myself more impressed by a metal one. I also feel like a retractible metal sword is the best of both worlds since it's extremely easy to hide and carry around, but it has the comfortable weight of a metal blade. As far as I know, hard energy blades have little to no weight and therefore require very different skills from traditional swordsmanship. Not to mention the fact that the weight of the blade can put some extra force behind your strikes. And it would also be a bad idea to twirl an energy blade around like cool people in movies since if your hand slips, it would be much easier to cut yourself in half than with a metal blade. Admittedly, there are some situations where a lightsaber would be more useful, but since I don't plan on getting into any of those situations, I would prefer to have a battle ready retractible metal blade than a lightsaber.