This was the trick for Maps!

implementations/rust/oo/Cargo.toml

@@ -7,6 +7,7 @@ edition = "2021"
 
 [dependencies]
 base64 = "0.13"
+bytemuck = "1.12"
 dtoa = "0.4"
 num = "0.4"
 regex = "1.5"

implementations/rust/oo/src/lib.rs

@@ -1,4 +1,6 @@
-use std::borrow::Cow;
+use bytemuck::TransparentWrapper;
+
+use std::borrow::{Cow, Borrow};
 use std::cmp::Ordering;
 use std::fmt::Debug;
 use std::hash::{Hash, Hasher};
@@ -74,7 +76,7 @@ pub trait Value<D: Domain>: Debug {
     fn has(&self, _v: &dyn Value<D>) -> bool { false }
 
     fn is_dictionary(&self) -> bool { false }
-    fn get(&self, _k: &(dyn Value<D> + 'static)) -> Option<&dyn Value<D>> { None }
+    fn get(&self, _k: &dyn Value<D>) -> Option<&dyn Value<D>> { None }
     fn entries(&self) -> Option<Box<dyn Iterator<Item = (&dyn Value<D>, &dyn Value<D>)> + '_>> { None }
 
     fn is_embedded(&self) -> bool { false }
@@ -105,7 +107,7 @@ impl<'a, D: Domain, V: Value<D> + ?Sized> Value<D> for &'a V {
     fn is_set(&self) -> bool { (*self).is_set() }
     fn has(&self, v: &dyn Value<D>) -> bool { (*self).has(v) }
     fn is_dictionary(&self) -> bool { (*self).is_dictionary() }
-    fn get(&self, k: &(dyn Value<D> + 'static)) -> Option<&dyn Value<D>> { (*self).get(k) }
+    fn get(&self, k: &dyn Value<D>) -> Option<&dyn Value<D>> { (*self).get(k) }
     fn entries(&self) -> Option<Box<dyn Iterator<Item = (&dyn Value<D>, &dyn Value<D>)> + '_>> { (*self).entries() }
     fn is_embedded(&self) -> bool { (*self).is_embedded() }
     fn embedded(&self) -> Option<Cow<'_, D>> { (*self).embedded() }
@@ -130,7 +132,7 @@ impl<D: Domain> Value<D> for Box<dyn Value<D>> {
     fn is_set(&self) -> bool { self.as_ref().is_set() }
     fn has(&self, v: &dyn Value<D>) -> bool { self.as_ref().has(v) }
     fn is_dictionary(&self) -> bool { self.as_ref().is_dictionary() }
-    fn get(&self, k: &(dyn Value<D> + 'static)) -> Option<&dyn Value<D>> { self.as_ref().get(k) }
+    fn get(&self, k: &dyn Value<D>) -> Option<&dyn Value<D>> { self.as_ref().get(k) }
     fn entries(&self) -> Option<Box<dyn Iterator<Item = (&dyn Value<D>, &dyn Value<D>)> + '_>> { self.as_ref().entries() }
     fn is_embedded(&self) -> bool { self.as_ref().is_embedded() }
     fn embedded(&self) -> Option<Cow<'_, D>> { self.as_ref().embedded() }
@@ -341,13 +343,28 @@ impl<D: Domain> Value<D> for Set<Box<dyn Value<D>>> {
     }
 }
 
+#[derive(PartialEq, Eq, PartialOrd, Ord)]
+#[repr(transparent)]
+struct Key<'a, D: Domain>(dyn Value<D> + 'a);
+
+// Many thanks to SkiFire13 and the other participants in
+// https://users.rust-lang.org/t/is-the-lifetime-of-a-btreemap-get-result-attached-to-the-key-as-well-as-the-map/83568/7
+// for the idea of using TransparentWrapper here.
+//
+unsafe impl<'a, D: Domain> TransparentWrapper<dyn Value<D> + 'a> for Key<'a, D> {}
+impl<'a, 'b: 'a, D: Domain> Borrow<Key<'a, D>> for Box<dyn Value<D> + 'b> {
+    fn borrow(&self) -> &Key<'a, D> {
+        Key::wrap_ref(&**self)
+    }
+}
+
 impl<D: Domain, V: Value<D>> Value<D> for Map<Box<dyn Value<D>>, V> {
     fn value_class(&self) -> ValueClass { ValueClass::Compound(CompoundClass::Dictionary) }
     fn is_dictionary(&self) -> bool { true }
     fn len(&self) -> Option<usize> { Some(self.len()) }
     fn has(&self, v: &dyn Value<D>) -> bool { self.contains_key(v) }
-    fn get(&self, k: &(dyn Value<D> + 'static)) -> Option<&dyn Value<D>> {
-        match Map::get(self, k) {
+    fn get(&self, k: &dyn Value<D>) -> Option<&dyn Value<D>> {
+        match Map::get(self, Key::wrap_ref(&k)) {
             Some(v) => Some(v),
             None => None,
         }
@@ -395,7 +412,7 @@ impl<D: Domain, V: Value<D>> Value<D> for Annotations<D, V> {
     fn is_set(&self) -> bool { self.value().is_set() }
     fn has(&self, v: &dyn Value<D>) -> bool { self.value().has(v) }
     fn is_dictionary(&self) -> bool { self.value().is_dictionary() }
-    fn get(&self, k: &(dyn Value<D> + 'static)) -> Option<&dyn Value<D>> { self.value().get(k) }
+    fn get(&self, k: &dyn Value<D>) -> Option<&dyn Value<D>> { self.value().get(k) }
     fn entries(&self) -> Option<Box<dyn Iterator<Item = (&dyn Value<D>, &dyn Value<D>)> + '_>> { self.value().entries() }
     fn is_embedded(&self) -> bool { self.value().is_embedded() }
     fn embedded(&self) -> Option<Cow<'_, D>> { self.value().embedded() }
@@ -433,7 +450,7 @@ mod demo {
     use crate::*;
 
     fn getit<'a>(d: &'a dyn Value<NoValue>, k: &str) -> Option<&'a dyn Value<NoValue>> {
-        d.get(&k as &(dyn Value<NoValue> + 'static))
+        d.get(&k)
     }
 
     #[test] fn a() {
@@ -457,7 +474,7 @@ mod demo {
         //     for line in std::io::stdin().lock().lines() {
         //         let line = line.unwrap();
         //         let val = w.get(&line);
-        //         println!("{:?} = {:?}", line, val);
+        //         println!("{:?} ==> {:?} == {:?}", line, val, getit(&v, &line));
         //     }
         // }
     }