Unboxed closures

A relatively complete description of by reference closures that aims to encompass entirety of current thinking, except for bound lifetimes.

cc @pcwalton
On Mon, Jun 16, 2014 at 01:23:42PM -0700, Felix S Klock II wrote:
> Each of the above trait references has neither a leading `&` nor a leading `impl` (i.e. the syntax from #105).

Right, because they are trait references.

> Does that mean that someone using the `|T1..Tn|: K -> R` syntax
> (i.e. our current syntax and soon-to-be "sugar") would need to start
> using a leading `&` or `impl` ?

Yes.

> Or is this relying in some way on passing an unsized type by value?

Originally I wanted this, but we've dropped the notion.