In a british movie, a boy is asking an old military man about his sword:
-Boy: Is that the sword you used in battles Mr.Poulter. Could I see it?
-The man(Mr.Poulter): Very dangerous weapon, my lad. An edge as what you could shave with.
The structure "...as what..." in the sentence caught my attention. I have never seen such a structure for comparison. We were taught at school that we should use "so+adjective+that" structure for such comparisons.
I think the man means "The edge is so sharp that you could even use it for shaving".(Or The edge is as sharp as a razor).
If what I understand is correct, then can we say "..as what..." structure is a short form of "...so+adjective+that..." structure, which we were taught at school.