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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.
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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;
}
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.
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A "boring" constraint (caused by the given location) is one that
the user probably doesn't want to see described in diagnostics,
because it is kind of an artifact of the type system setup.
Example: x = Foo { field: y }
technically creates
intermediate regions representing the "type of Foo { field: y }
", and data flows from y
into those variables, but they
are not very interesting. The assignment into x
on the other
hand might be.
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An important outlives constraint (caused by the given
location) is one that would be useful to highlight in
diagnostics, because it represents a point where references
flow from one spot to another (e.g., x = y
)
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🔬 This is a nightly-only experimental API. (rustc_private
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Gets a span representing the location.
Performs copy-assignment from source
. Read more
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
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
This method returns an Ordering
between self
and other
. Read more
fn max(self, other: Self) -> Self | 1.21.0 [src] |
Compares and returns the maximum of two values. Read more
fn min(self, other: Self) -> Self | 1.21.0 [src] |
Compares and returns the minimum of two values. Read more
Feeds this value into the given [Hasher
]. Read more
Feeds a slice of this type into the given [Hasher
]. Read more
Formats the value using the given formatter. Read more
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Creates owned data from borrowed data, usually by cloning. Read more
🔬 This is a nightly-only experimental API. (toowned_clone_into
)
recently added
Uses borrowed data to replace owned data, usually by cloning. Read more
🔬 This is a nightly-only experimental API. (try_from
)
The type returned in the event of a conversion error.
🔬 This is a nightly-only experimental API. (try_from
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Immutably borrows from an owned value. Read more
type Error = <U as TryFrom<T>>::Error
🔬 This is a nightly-only experimental API. (try_from
)
The type returned in the event of a conversion error.
🔬 This is a nightly-only experimental API. (try_from
)
Mutably borrows from an owned value. Read more
🔬 This is a nightly-only experimental API. (get_type_id
)
this method will likely be replaced by an associated static
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Create an error for a missing method specialization. Defaults to panicking with type, trait & method names. S
is the encoder/decoder state type, T
is the type being encoded/decoded, and the arguments are the names of the trait and method that should've been overridden. Read more
🔬 This is a nightly-only experimental API. (rustc_private
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🔬 This is a nightly-only experimental API. (rustc_private
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