# HG changeset patch
# User Tuomo Valkonen <tuomov@iki.fi>
# Date 1731203672 18000
# Node ID 3f3e00e817552e9b7c28481ea2c7b279370104b7
# Parent  a0db98c16ab58e1e1da2fe5451a970ec5a90dff1
Some Differential GATs

diff -r a0db98c16ab5 -r 3f3e00e81755 src/mapping.rs
--- a/src/mapping.rs	Sat Nov 09 20:36:23 2024 -0500
+++ b/src/mapping.rs	Sat Nov 09 20:54:32 2024 -0500
@@ -3,7 +3,7 @@
 */
 
 use std::marker::PhantomData;
-use crate::types::{Float};
+use crate::types::Float;
 use serde::Serialize;
 use crate::loc::Loc;
 
@@ -52,10 +52,10 @@
 /// Automatically implemented shorthand for referring to differentiable [`Mapping`]s from
 /// [`Loc<F, N>`] to `F`.
 pub trait DifferentiableRealMapping<F : Float, const N : usize>
-: DifferentiableMapping<Loc<F, N>, Codomain = F, Differential=Loc<F, N>> {}
+: DifferentiableMapping<Loc<F, N>, Codomain = F, DerivativeDomain=Loc<F, N>> {}
 
 impl<F : Float, T, const N : usize> DifferentiableRealMapping<F, N> for T
-where T : DifferentiableMapping<Loc<F, N>, Codomain = F, Differential=Loc<F, N>> {}
+where T : DifferentiableMapping<Loc<F, N>, Codomain = F, DerivativeDomain=Loc<F, N>> {}
 
 
 /// A helper trait alias for referring to [`Mapping`]s from [`Loc<F, N>`] to [`Loc<F, M>`].
@@ -80,29 +80,38 @@
 /// This is automatically implemented when the relevant [`Differentiate`] are implemented.
 pub trait DifferentiableMapping<Domain>
 : Mapping<Domain>
-  + Differentiable<Domain, Derivative=Self::Differential>
-  + for<'a> Differentiable<&'a Domain, Derivative=Self::Differential> {
-    type Differential;
+  + Differentiable<Domain, Derivative=Self::DerivativeDomain>
+  + for<'a> Differentiable<&'a Domain, Derivative=Self::DerivativeDomain> {
+    type DerivativeDomain;
+    type Differential : Mapping<Domain, Codomain=Self::DerivativeDomain>;
+    type DifferentialRef<'b> : Mapping<Domain, Codomain=Self::DerivativeDomain> where Self : 'b;
 
     /// Form the differential mapping of `self`.
-    fn diff(self) -> Differential<Domain, Self> {
+    fn diff(self) -> Self::Differential;
+    /// Form the differential mapping of `self`.
+    fn diff_ref(&self) -> Self::DifferentialRef<'_>;
+}
+
+
+impl<Domain, Derivative, T> DifferentiableMapping<Domain> for T
+where T : Mapping<Domain>
+          + Differentiable<Domain, Derivative=Derivative>
+          + for<'a> Differentiable<&'a Domain,Derivative=Derivative> {
+    type DerivativeDomain = Derivative;
+    type Differential = Differential<Domain, Self>;
+    type DifferentialRef<'b> = Differential<Domain, Ref<'b, Self>> where Self : 'b;
+    
+    /// Form the differential mapping of `self`.
+    fn diff(self) -> Self::Differential {
         Differential{ g : self, _space : PhantomData }
     }
 
     /// Form the differential mapping of `self`.
-    fn diff_ref(&self) -> Differential<Domain, Ref<'_, Self>> {
+    fn diff_ref(&self) -> Self::DifferentialRef<'_> {
         Differential{ g : Ref(self), _space : PhantomData }
     }
 }
 
-
-impl<Domain, Differential, T> DifferentiableMapping<Domain> for T
-where T : Mapping<Domain>
-          + Differentiable<Domain, Derivative=Differential>
-          + for<'a> Differentiable<&'a Domain, Derivative=Differential> {
-    type Differential = Differential;
-}
-
 /// A sum of [`Mapping`]s.
 #[derive(Serialize, Debug, Clone)]
 pub struct Sum<Domain, M : Mapping<Domain>> {
@@ -146,10 +155,10 @@
 impl<Domain, M> Differentiable<Domain> for Sum<Domain, M>
 where M : DifferentiableMapping<Domain>,
       M :: Codomain : std::iter::Sum,
-      M :: Differential : std::iter::Sum,
+      M :: DerivativeDomain : std::iter::Sum,
       Domain : Copy {
 
-    type Derivative = M::Differential;
+    type Derivative = M::DerivativeDomain;
 
     fn differential(&self, x : Domain) -> Self::Derivative {
         self.components.iter().map(|c| c.differential(x)).sum()
@@ -163,19 +172,19 @@
 }
 
 impl<X, G : DifferentiableMapping<X>> Apply<X> for Differential<X, G> {
-    type Output = G::Differential;
+    type Output = G::DerivativeDomain;
 
     #[inline]
-    fn apply(&self, x : X) -> G::Differential {
+    fn apply(&self, x : X) -> Self::Output {
         self.g.differential(x)
     }
 }
 
 impl<'a, X, G : DifferentiableMapping<X>> Apply<&'a X> for Differential<X, G> {
-    type Output = G::Differential;
+    type Output = G::DerivativeDomain;
 
     #[inline]
-    fn apply(&self, x : &'a X) -> G::Differential {
+    fn apply(&self, x : &'a X) -> Self::Output {
         self.g.differential(x)
     }
 }