diff -r 221728aeeb7e -r fa8df5a14486 src/instance.rs
--- a/src/instance.rs	Wed Sep 03 19:55:05 2025 -0500
+++ b/src/instance.rs	Wed Sep 03 20:19:41 2025 -0500
@@ -328,14 +328,18 @@
 {
     /// Decomposes self according to `decomposer`, and evaluate `f` on the result.
     /// Consumes self.
+    #[inline]
     fn eval_decompose<'b, R>(self, f: impl FnOnce(D::Decomposition<'b>) -> R) -> R
     where
         X: 'b,
-        Self: 'b;
+        Self: 'b,
+    {
+        f(self.decompose())
+    }
 
     /// Does a light decomposition of self `decomposer`, and evaluates `f` on the result.
     /// Does not consume self.
-    fn eval_ref_decompose<'b, R>(&'b self, f: impl FnOnce(D::Reference<'b>) -> R) -> R
+    fn eval_ref<'b, R>(&'b self, f: impl FnOnce(D::Reference<'b>) -> R) -> R
     where
         X: 'b,
         Self: 'b;
@@ -345,7 +349,7 @@
     fn either<'b, R>(
         self,
         f: impl FnOnce(D::Decomposition<'b>) -> R,
-        g: impl FnOnce(D::Reference<'b>) -> R,
+        _g: impl FnOnce(D::Reference<'b>) -> R,
     ) -> R
     where
         X: 'b,
@@ -357,6 +361,10 @@
     /// Returns an owned instance of `X`, cloning or converting non-true instances when necessary.
     fn own(self) -> X::Principal;
 
+    fn decompose<'b>(self) -> D::Decomposition<'b>
+    where
+        Self: 'b;
+
     /// Returns an owned instance or reference to `X`, converting non-true instances when necessary.
     ///
     /// Default implementation uses [`Self::own`]. Consumes the input.
@@ -387,16 +395,7 @@
     }
 
     #[inline]
-    fn eval_decompose<'b, R>(self, f: impl FnOnce(MyCow<'b, X>) -> R) -> R
-    where
-        X: 'b,
-        Self: 'b,
-    {
-        f(MyCow::Owned(self))
-    }
-
-    #[inline]
-    fn eval_ref_decompose<'b, R>(&'b self, f: impl FnOnce(&'b X) -> R) -> R
+    fn eval_ref<'b, R>(&'b self, f: impl FnOnce(&'b X) -> R) -> R
     where
         X: 'b,
         Self: 'b,
@@ -416,6 +415,14 @@
     {
         self.cow_owned()
     }
+
+    #[inline]
+    fn decompose<'b>(self) -> MyCow<'b, X>
+    where
+        Self: 'b,
+    {
+        MyCow::Owned(self)
+    }
 }
 
 impl<'a, X: Space> Instance<X, BasicDecomposition> for &'a X {
@@ -428,16 +435,7 @@
     }
 
     #[inline]
-    fn eval_decompose<'b, R>(self, f: impl FnOnce(MyCow<'b, X>) -> R) -> R
-    where
-        X: 'b,
-        Self: 'b,
-    {
-        f(MyCow::Borrowed(self))
-    }
-
-    #[inline]
-    fn eval_ref_decompose<'b, R>(&'b self, f: impl FnOnce(&'b X) -> R) -> R
+    fn eval_ref<'b, R>(&'b self, f: impl FnOnce(&'b X) -> R) -> R
     where
         X: 'b,
         Self: 'b,
@@ -457,6 +455,14 @@
     {
         self.cow_owned()
     }
+
+    #[inline]
+    fn decompose<'b>(self) -> MyCow<'b, X>
+    where
+        Self: 'b,
+    {
+        MyCow::Borrowed(self)
+    }
 }
 
 impl<'a, X: Space> Instance<X, BasicDecomposition> for &'a mut X {
@@ -469,16 +475,7 @@
     }
 
     #[inline]
-    fn eval_decompose<'b, R>(self, f: impl FnOnce(MyCow<'b, X>) -> R) -> R
-    where
-        X: 'b,
-        Self: 'b,
-    {
-        f(EitherDecomp::Borrowed(self))
-    }
-
-    #[inline]
-    fn eval_ref_decompose<'b, R>(&'b self, f: impl FnOnce(&'b X) -> R) -> R
+    fn eval_ref<'b, R>(&'b self, f: impl FnOnce(&'b X) -> R) -> R
     where
         X: 'b,
         Self: 'b,
@@ -498,6 +495,14 @@
     {
         self.cow_owned()
     }
+
+    #[inline]
+    fn decompose<'b>(self) -> MyCow<'b, X>
+    where
+        Self: 'b,
+    {
+        MyCow::Borrowed(self)
+    }
 }
 
 impl<'a, X: Space> Instance<X, BasicDecomposition> for MyCow<'a, X> {
@@ -510,16 +515,7 @@
     }
 
     #[inline]
-    fn eval_decompose<'b, R>(self, f: impl FnOnce(MyCow<'b, X>) -> R) -> R
-    where
-        X: 'b,
-        Self: 'b,
-    {
-        f(self)
-    }
-
-    #[inline]
-    fn eval_ref_decompose<'b, R>(&'b self, f: impl FnOnce(&'b X) -> R) -> R
+    fn eval_ref<'b, R>(&'b self, f: impl FnOnce(&'b X) -> R) -> R
     where
         X: 'b,
         Self: 'b,
@@ -542,6 +538,14 @@
     {
         self.cow_owned()
     }
+
+    #[inline]
+    fn decompose<'b>(self) -> MyCow<'b, X>
+    where
+        Self: 'b,
+    {
+        self
+    }
 }
 
 /// Marker type for mutable decompositions to be used with [`InstanceMut`].