Part 2: Use ValueRc in InternSet.

We haven't observed performance issues using `Arc` instead of `Rc`,
and we want to be able to include things that are interned (including,
soon, `TempId` instances) in errors coming out of the
transactor.  (And `Rc` isn't `Sync`, so it can't be included in errors
directly.)

db/src/internal_types.rs

@@ -17,7 +17,6 @@ use std::collections::{
     BTreeSet,
     HashMap,
 };
-use std::rc::Rc;
 
 use mentat_core::KnownEntid;
 
@@ -27,6 +26,14 @@ use edn;
 use edn::{
     SpannedValue,
     ValueAndSpan,
+    ValueRc,
+};
+use edn::entities;
+use edn::entities::{
+    EntityPlace,
+    OpType,
+    TempId,
+    TxFunction,
 };
 
 use errors;
@@ -47,13 +54,6 @@ use types::{
     TypedValue,
     ValueType,
 };
-use edn::entities;
-use edn::entities::{
-    EntityPlace,
-    OpType,
-    TempId,
-    TxFunction,
-};
 
 impl TransactableValue for ValueAndSpan {
     fn into_typed_value(self, schema: &Schema, value_type: ValueType) -> Result<TypedValue> {
@@ -150,10 +150,10 @@ use self::Either::*;
 pub type KnownEntidOr<T> = Either<KnownEntid, T>;
 pub type TypedValueOr<T> = Either<TypedValue, T>;
 
-pub type TempIdHandle = Rc<TempId>;
+pub type TempIdHandle = ValueRc<TempId>;
 pub type TempIdMap = HashMap<TempIdHandle, KnownEntid>;
 
-pub type LookupRef = Rc<AVPair>;
+pub type LookupRef = ValueRc<AVPair>;
 
 /// Internal representation of an entid on its way to resolution.  We either have the simple case (a
 /// numeric entid), a lookup-ref that still needs to be resolved (an atomized [a v] pair), or a temp

db/src/tx.rs

@@ -56,9 +56,6 @@ use std::collections::{
 use std::iter::{
     once,
 };
-use std::rc::{
-    Rc,
-};
 
 use db;
 use db::{
@@ -68,6 +65,7 @@ use db::{
 use edn::{
     InternSet,
     Keyword,
+    ValueRc,
 };
 use entids;
 use errors;
@@ -303,7 +301,7 @@ impl<'conn, 'a, W> Tx<'conn, 'a, W> where W: TransactWatcher {
                 Ok(self.lookup_refs.intern((lr_a, lr_typed_value)))
             }
 
-            fn intern_temp_id(&mut self, temp_id: TempId) -> Rc<TempId> {
+            fn intern_temp_id(&mut self, temp_id: TempId) -> ValueRc<TempId> {
                 self.temp_ids.intern(temp_id)
             }
 

edn/src/intern_set.rs

@@ -12,7 +12,10 @@
 
 use std::collections::HashSet;
 use std::hash::Hash;
-use std::rc::Rc;
+
+use ::{
+    ValueRc,
+};
 
 /// An `InternSet` allows to "intern" some potentially large values, maintaining a single value
 /// instance owned by the `InternSet` and leaving consumers with lightweight ref-counted handles to
@@ -23,7 +26,7 @@ use std::rc::Rc;
 /// See https://en.wikipedia.org/wiki/String_interning for discussion.
 #[derive(Clone, Debug, Default, Eq, PartialEq)]
 pub struct InternSet<T> where T: Eq + Hash {
-    pub inner: HashSet<Rc<T>>,
+    pub inner: HashSet<ValueRc<T>>,
 }
 
 impl<T> InternSet<T> where T: Eq + Hash {
@@ -40,13 +43,12 @@ impl<T> InternSet<T> where T: Eq + Hash {
     /// Intern a value, providing a ref-counted handle to the interned value.
     ///
     /// ```
-    /// use std::rc::Rc;
+    /// use edn::{InternSet, ValueRc};
-    /// use edn::intern_set::InternSet;
     ///
     /// let mut s = InternSet::new();
     ///
     /// let one = "foo".to_string();
-    /// let two = Rc::new("foo".to_string());
+    /// let two = ValueRc::new("foo".to_string());
     ///
     /// let out_one = s.intern(one);
     /// assert_eq!(out_one, two);
@@ -57,8 +59,8 @@ impl<T> InternSet<T> where T: Eq + Hash {
     /// assert_eq!(1, s.inner.len());
     /// // assert!(&out_one.ptr_eq(&out_two));   // Nightly-only.
     /// ```
-    pub fn intern<R: Into<Rc<T>>>(&mut self, value: R) -> Rc<T> {
+    pub fn intern<R: Into<ValueRc<T>>>(&mut self, value: R) -> ValueRc<T> {
-        let key: Rc<T> = value.into();
+        let key: ValueRc<T> = value.into();
         if self.inner.insert(key.clone()) {
             key
         } else {