Enum rustc_mir::borrow_check::nll::type_check::Locations[][src]

pub enum Locations {
    All,
    Pair {
        from_location: Location,
        at_location: Location,
    },
}
🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

The Locations type summarizes where region constraints are required to hold. Normally, this is at a particular point which created the obligation, but for constraints that the user gave, we want the constraint to hold at all points.

Variants

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

Indicates that a type constraint should always be true. This is particularly important in the new borrowck analysis for things like the type of the return slot. Consider this example:

fn foo<'a>(x: &'a u32) -> &'a u32 {
    let y = 22;
    return &y; // error
}

Here, we wind up with the signature from the return type being something like &'1 u32 where '1 is a universal region. But the type of the return slot _0 is something like &'2 u32 where '2 is an existential region variable. The type checker requires that &'2 u32 = &'1 u32 -- but at what point? In the older NLL analysis, we required this only at the entry point to the function. By the nature of the constraints, this wound up propagating to all points reachable from start (because '1 -- as a universal region -- is live everywhere). In the newer analysis, though, this doesn't work: _0 is considered dead at the start (it has no usable value) and hence this type equality is basically a no-op. Then, later on, when we do _0 = &'3 y, that region '3 never winds up related to the universal region '1 and hence no error occurs. Therefore, we use Locations::All instead, which ensures that the '1 and '2 are equal everything. We also use this for other user-given type annotations; e.g., if the user wrote let mut x: &'static u32 = ..., we would ensure that all values assigned to x are of 'static lifetime.

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

Fields of Pair

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

The location in the MIR that generated these constraints. This is intended for error reporting and diagnosis; the constraints may take effect at a distinct spot.

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

The constraints must be met at this location. In terms of the NLL RFC, when you have a constraint R1: R2 @ P, this field is the P value.

Methods

impl Locations
[src]

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

Trait Implementations

impl Copy for Locations
[src]

impl Clone for Locations
[src]

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

impl Debug for Locations
[src]

Formats the value using the given formatter. Read more

impl ToLocations for Locations
[src]

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

Auto Trait Implementations

impl Send for Locations

impl Sync for Locations