On the front of this Glock 17 is a standoff device which slides onto the accessory rail.The concept behind a standoff is that the muzzle of the gun can be pressed against the target/adversary's body and not cause the gun to go out off battery(push the slide back so that the gun will not function).The original Springfield XD's had a recoil spring rod that protruded from the front of the gun and is said to act as a standoff.I did several simulations with my XD .45 ACP and found that the stand-off/rod only worked against a hard surface.If you pressed it against something relatively soft like a human body ,it simply didn't work. The one pictured on the Glock looks like it would work although I would have to run through some practice simulations first.A tactical light that protrudes beyond the muzzle might work well also.
Many people think a standoff is unnecessary,but self-defense situations often take place at extremely close ranges and you might have to take a shot at muzzle contact distances.I was talking to Massad Ayoob about firearms choices for hiking in area's where there might be the possibility of encountering large predator's such as Bears.Mas said he definitely preferred a Revolver(.44 Mag 4"Barrel 629 Mountain Gun) due to the fact that Bear Attacks happen sudden & fast & you might find yourself at Muzzle contact distances with a Bear on top of you & a semi-auto just work if it's pressed against the animals hide.
I think the same may occur with two legged predators.I could imagine a rapist or intruder being held at gunpoint by his intended Female victim & attempting a disarm.Or even being ambushed by a mugger or other garden variety psychopath and find yourself on the ground with the bad guy on top of you.In these situations I do indeed prefer the short barreled revolver because even a standoff,it's to easy for the BG to grab the slide etc. Still the idea of a standoff on a semi-auto is still worth exploring and while it still won't allow you to fire it from a coat pocket like a snubbie, it may solve the muzzle contact shot problem.