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

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

Gets a span representing the location.

Trait Implementations

Returns a copy of the value. Read more
Performs copy-assignment from source. Read more
Formats the value using the given formatter. Read more
Feeds this value into the given Hasher. Read more
Feeds a slice of this type into the given Hasher. Read more
This method returns an Ordering between self and other. Read more
Compares and returns the maximum of two values. Read more
Compares and returns the minimum of two values. Read more
Restrict a value to a certain interval. Read more
This method tests for self and other values to be equal, and is used by ==. Read more
This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason. Read more
This method returns an ordering between self and other values if one exists. Read more
This method tests less than (for self and other) and is used by the < operator. Read more
This method tests less than or equal to (for self and other) and is used by the <= operator. Read more
This method tests greater than (for self and other) and is used by the > operator. Read more
This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The resulting type after obtaining ownership.
Creates owned data from borrowed data, usually by cloning. Read more
Uses borrowed data to replace owned data, usually by cloning. Read more
The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference’s “Type Layout” chapter for details on type layout guarantees.

Size: 16 bytes

Size for each variant:

  • All: 8 bytes
  • Single: 16 bytes