Update MIR `Place` description

[pierwill]

It looks like this is out-of-date, since Place is a struct, not an enum.

rustc-dev-guide/src/mir/index.md

Lines 238 to 247 in 9d20811

	- **Places** are identified by the enum [`Place`]. There are a few
	variants:
	- Local variables like `_1`
	- Static variables `FOO`
	- **Projections**, which are fields or other things that "project
	out" from a base place. These are represented by the type
	[`ProjectionElem`]. So e.g. the place `_1.f` is a projection,
	with `f` being the "projection element" and `_1` being the base
	path. `*_1` is also a projection, with the `*` being represented
	by the [`ProjectionElem::Deref`] element.

[tshepang]

@spastorino this is something you worked on... would update it, but am not familiar enough

[spastorino]

Yes Place was an enum and if I'm not wrong I've changed it a long while ago to be an struct. By looking at the source code is still a struct https://github.com/rust-lang/rust/blob/7e54847de328a7346c588720f616bf1fcdf609d5/compiler/rustc_middle/src/mir/syntax.rs#L792-L797 so we can update this section of the guide yeah.

[tshepang]

@spastorino is the description (the 3 bullet points) still accurate

[spastorino]

It seems to me that things have changed a bit since I've last checked it. I don't think statics are handled through it, I'd change the more abstract ProjectionElem to PlaceElem and I don't think Deref is handled through it anymore neither. To be honest, I didn't check the code to say what I'm saying, I'm kind of playing by ear.

cc @oli-obk

[oli-obk]

other than that Deref still exists (it's in the process of being removed), everything you said is correct