PartialOrder with Rhs type parameter (#565)

* PartialOrder generic over right-hand side

Change the `PartialOrder` trait to have an optional right-hand side type.
This allows us to implement partial order for unequal types, which comes
in handy when working with complex timestamp times that a container might
store as a GAT instead of the actual type.

Signed-off-by: Moritz Hoffmann <[email protected]>

* Address feedback

Signed-off-by: Moritz Hoffmann <[email protected]>

---------

Signed-off-by: Moritz Hoffmann <[email protected]>

timely/src/order.rs

@@ -5,13 +5,13 @@
 /// This trait is distinct from Rust's `PartialOrd` trait, because the implementation
 /// of that trait precludes a distinct `Ord` implementation. We need an independent
 /// trait if we want to have a partially ordered type that can also be sorted.
-pub trait PartialOrder : Eq {
+pub trait PartialOrder<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     /// Returns true iff one element is strictly less than the other.
-    fn less_than(&self, other: &Self) -> bool {
+    fn less_than(&self, other: &Rhs) -> bool {
         self.less_equal(other) && self != other
     }
     /// Returns true iff one element is less than or equal to the other.
-    fn less_equal(&self, other: &Self) -> bool;
+    fn less_equal(&self, other: &Rhs) -> bool;
 }
 
 /// A type that is totally ordered.
@@ -97,9 +97,14 @@ mod product {
     }
 
     use super::PartialOrder;
-    impl<TOuter: PartialOrder, TInner: PartialOrder> PartialOrder for Product<TOuter, TInner> {
+    impl<TOuter, TOuter2, TInner, TInner2> PartialOrder<Product<TOuter2, TInner2>> for Product<TOuter, TInner>
+    where
+        TOuter: PartialOrder<TOuter2>,
+        TInner: PartialOrder<TInner2>,
+        Self: PartialEq<Product<TOuter2, TInner2>>,
+    {
         #[inline]
-        fn less_equal(&self, other: &Self) -> bool {
+        fn less_equal(&self, other: &Product<TOuter2, TInner2>) -> bool {
             self.outer.less_equal(&other.outer) && self.inner.less_equal(&other.inner)
         }
     }
@@ -189,9 +194,14 @@ mod product {
 mod tuple {
 
     use super::PartialOrder;
-    impl<TOuter: PartialOrder, TInner: PartialOrder> PartialOrder for (TOuter, TInner) {
+    impl<TOuter, TOuter2, TInner, TInner2> PartialOrder<(TOuter2, TInner2)> for (TOuter, TInner)
+    where
+        TOuter: PartialOrder<TOuter2>,
+        TInner: PartialOrder<TInner2>,
+        (TOuter, TInner): PartialEq<(TOuter2, TInner2)>,
+    {
         #[inline]
-        fn less_equal(&self, other: &Self) -> bool {
+        fn less_equal(&self, other: &(TOuter2, TInner2)) -> bool {
             // We avoid Rust's `PartialOrd` implementation, for reasons of correctness.
             self.0.less_than(&other.0) || (self.0.eq(&other.0) && self.1.less_equal(&other.1))
         }

timely/src/progress/frontier.rs

@@ -69,6 +69,32 @@ impl<T: PartialOrder> Antichain<T> {
         }
     }
 
+    /// Updates the `Antichain` if the element is not greater than or equal to some present element.
+    /// If the antichain needs updating, it uses the `to_owned` closure to convert the element into
+    /// a `T`.
+    ///
+    /// Returns true if element is added to the set
+    ///
+    /// # Examples
+    ///
+    ///```
+    /// use timely::progress::frontier::Antichain;
+    ///
+    /// let mut frontier = Antichain::new();
+    /// assert!(frontier.insert_with(&2, |x| *x));
+    /// assert!(!frontier.insert(3));
+    ///```
+    pub fn insert_with<O: PartialOrder<T>, F: FnOnce(&O) -> T>(&mut self, element: &O, to_owned: F) -> bool where T: PartialOrder<O> {
+        if !self.elements.iter().any(|x| x.less_equal(element)) {
+            self.elements.retain(|x| !element.less_equal(x));
+            self.elements.push(to_owned(element));
+            true
+        }
+        else {
+            false
+        }
+    }
+
     /// Reserves capacity for at least additional more elements to be inserted in the given `Antichain`
     pub fn reserve(&mut self, additional: usize) {
         self.elements.reserve(additional);
@@ -450,9 +476,9 @@ impl<T> MutableAntichain<T> {
     /// assert!(frontier.less_than(&2));
     ///```
     #[inline]
-    pub fn less_than(&self, time: &T) -> bool
+    pub fn less_than<O>(&self, time: &O) -> bool
     where
-        T: PartialOrder,
+        T: PartialOrder<O>,
     {
         self.frontier().less_than(time)
     }
@@ -470,9 +496,9 @@ impl<T> MutableAntichain<T> {
     /// assert!(frontier.less_equal(&2));
     ///```
     #[inline]
-    pub fn less_equal(&self, time: &T) -> bool
+    pub fn less_equal<O>(&self, time: &O) -> bool
     where
-        T: PartialOrder,
+        T: PartialOrder<O>,
     {
         self.frontier().less_equal(time)
     }
@@ -549,9 +575,9 @@ impl<T> MutableAntichain<T> {
     }
 
     /// Reports the count for a queried time.
-    pub fn count_for(&self, query_time: &T) -> i64
+    pub fn count_for<O>(&self, query_time: &O) -> i64
     where
-        T: Ord,
+        T: PartialEq<O>,
     {
         self.updates
             .unstable_internal_updates()
@@ -679,7 +705,7 @@ impl<'a, T: 'a> AntichainRef<'a, T> {
     }
 }
 
-impl<'a, T: 'a+PartialOrder> AntichainRef<'a, T> {
+impl<T> AntichainRef<'_, T> {
 
     /// Returns true if any item in the `AntichainRef` is strictly less than the argument.
     ///
@@ -694,7 +720,7 @@ impl<'a, T: 'a+PartialOrder> AntichainRef<'a, T> {
     /// assert!(frontier.less_than(&2));
     ///```
     #[inline]
-    pub fn less_than(&self, time: &T) -> bool {
+    pub fn less_than<O>(&self, time: &O) -> bool where T: PartialOrder<O> {
         self.iter().any(|x| x.less_than(time))
     }
 
@@ -711,7 +737,7 @@ impl<'a, T: 'a+PartialOrder> AntichainRef<'a, T> {
     /// assert!(frontier.less_equal(&1));
     /// assert!(frontier.less_equal(&2));
     ///```
-    pub fn less_equal(&self, time: &T) -> bool {
+    pub fn less_equal<O>(&self, time: &O) -> bool where T: PartialOrder<O> {
         self.iter().any(|x| x.less_equal(time))
     }
 }