[Pitch] SE-0377 Amendment: Making `borrowing` and `consuming` parameters require manual copying with a `copy` operator

[Joe_Groff]

@jayton

I think this is really surprising and will lead to confusion and people thinking they have guarantees that they don’t. If copying is explicit, I would expect to have to write let y = copy x.

That means something different, though, since let y = x would normally consume x in order to move it into y (and if x is a borrowing parameter, you would already have to write let y = copy x in order to make a copy that can be given to y). When we have the borrowing bindings, you would be able to use those instead of let or var as a way to bind to x, or part of x, without copying it and carrying the no-implicit-copy constraint forward.