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

pub enum Locations {
    All(Span),
    Single(Location),
}

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

All(Span)

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.

The span points to the place the constraint arose. For example, it points to the type in a user-given type annotation. If there's no sensible span then it's DUMMY_SP.

Single(Location)

An outlives constraint that only has to hold at a single location, usually it represents a point where references flow from one spot to another (e.g., x = y)

Implementations

impl Locations[src]

pub fn from_location(&self) -> Option<Location>[src]

pub fn span(&self, body: &Body<'_>) -> Span[src]

Gets a span representing the location.

Trait Implementations

impl Clone for Locations[src]

impl Copy for Locations[src]

impl Debug for Locations[src]

impl Eq for Locations[src]

impl Hash for Locations[src]

impl NormalizeLocation for Locations[src]

impl Ord for Locations[src]

impl PartialEq<Locations> for Locations[src]

impl PartialOrd<Locations> for Locations[src]

impl StructuralEq for Locations[src]

impl StructuralPartialEq for Locations[src]

Auto Trait Implementations

impl RefUnwindSafe for Locations

impl !Send for Locations

impl !Sync for Locations

impl Unpin for Locations

impl UnwindSafe for Locations

Blanket Implementations

impl<T> Any for T where
    T: 'static + ?Sized
[src]

impl<T> Borrow<T> for T where
    T: ?Sized
[src]

impl<T> BorrowMut<T> for T where
    T: ?Sized
[src]

impl<T> From<T> for T[src]

impl<T, U> Into<U> for T where
    U: From<T>, 
[src]

impl<T> ToOwned for T where
    T: Clone
[src]

type Owned = T

The resulting type after obtaining ownership.

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

impl<T> WithConstness for T[src]