Trait rustc_data_structures::unify::UnifyKey
source · pub trait UnifyKey: Copy + Clone + Debug + PartialEq<Self> {
type Value: UnifyValue;
fn index(&self) -> u32;
fn from_index(u: u32) -> Self;
fn tag() -> &'static str;
fn order_roots(
a: Self,
a_value: &Self::Value,
b: Self,
b_value: &Self::Value
) -> Option<(Self, Self)> { ... }
}
Expand description
This trait is implemented by any type that can serve as a type
variable. We call such variables unification keys. For example,
this trait is implemented by IntVid
, which represents integral
variables.
Each key type has an associated value type V
. For example, for
IntVid
, this is Option<IntVarValue>
, representing some
(possibly not yet known) sort of integer.
Clients are expected to provide implementations of this trait; you
can see some examples in the test
module.
Required Associated Types
type Value: UnifyValue
Required Methods
Provided Methods
sourcefn order_roots(
a: Self,
a_value: &Self::Value,
b: Self,
b_value: &Self::Value
) -> Option<(Self, Self)>
fn order_roots(
a: Self,
a_value: &Self::Value,
b: Self,
b_value: &Self::Value
) -> Option<(Self, Self)>
If true, then self
should be preferred as root to other
.
Note that we assume a consistent partial ordering, so
returning true implies that other.prefer_as_root_to(self)
would return false. If there is no ordering between two keys
(i.e., a.prefer_as_root_to(b)
and b.prefer_as_root_to(a)
both return false) then the rank will be used to determine the
root in an optimal way.
NB. The only reason to implement this method is if you want to
control what value is returned from find()
. In general, it
is better to let the unification table determine the root,
since overriding the rank can cause execution time to increase
dramatically.