lvalue and rvalue should be documented as well

[shepmaster]

No description provided.

[RalfJung]

Please, let's call them "place" and... "operand" or "value" or so. We probably have to mention "lvalue" in the description of "place" because it is used in C/C++, but it is not a great name.

[shepmaster]

I think whatever the canonical Rust name becomes, you will want these two documented, even if only as redirects to the proper name. Documenting what they are and picking a name for them can be orthogonal.

[steveklabnik]

We explicitly removed rvalue and lvalue from all Rust docs, in favor of 'place expressions' and 'value expressions' in all documentation a while back: https://doc.rust-lang.org/reference/expressions.html?highlight=place,exp#place-expressions-and-value-expressions

[RalfJung]

At least I was not talking about expressions though, but about the "thing" they evaluate to. 3+4 might be a "value expression", I guess, but it computes to "7" and that's a value, no further computation necessary.

I guess it would be consistent then to say that place expressions evaluate to a place, and value expressions evaluate to a value.

[strega-nil]

Another important thing is that place expressions can also evaluate to a value, and value expressions can evaluate to a place, if necessary.

First, it's important to note that there are 2 axes on which places can be put - the immutable/mutable axis, the owned/borrowed axis, and the initialized axis (ignored for this comment).

Place-to-value conversion is allowed when, given a place expression e of type T:

• T: Copy
• e is owned

Value-to-place conversion is allowed for all values (afaik), and results in a mutable, owned place expression.

[shepmaster]

To be clear, this is just a request that these terms be documented, just like the existing requests for terms. It seems like all of the discussion y'all are having will be lost / not-easily findable when this PR is merged. Perhaps it's appropriate to move that discussion into an issue?

[avadacatavra]

we can also just have something like

• lvalue/place
  if these are equivalent terms. i'd be in favor of having some disambiguation here (since i have no clue what any of these things mean in any forms :p)

[strega-nil]

@avadacatavra yeah, the term across the languages is lvalue (C), place (Rust), and glvalue (C++). Basically, it means an expression that refers to a location, as opposed to just a value:

fn main() {
  0; // value expression - 0 is not a place
  let x = 0;
  x; // place expression - x is a place
}

[avadacatavra]

i'd be fine if we wanted to add that to this PR 💯

[avadacatavra]

I'm going to merge this and we can define at some point in time