I've been writing rust since just before 1.0 and I've never written a type signature like that. I understand it just fine (even though it is invalid, I get what

I've been writing rust since just before 1.0 and I've never written a type signature like that. I understand it just fine (even though it is invalid, I get what they're saying), but yeah, never needed it. It's both a good and bad thing that rust has these sort of deep areas where 95% of users won't ever have to go - Pin being another example. I think it's much more good than bad though.