From afcf3bca3e57ab2b36bad8e3f62acc95a81a30fa Mon Sep 17 00:00:00 2001
From: Stepan Koltsov <stepan.koltsov@gmail.com>
Date: Sun, 20 Oct 2024 18:23:58 +0100
Subject: [PATCH] Replace TwoIterators with Either in bevy_animation

---
 crates/bevy_animation/Cargo.toml         |  1 +
 crates/bevy_animation/src/gltf_curves.rs | 33 +++++-------------------
 2 files changed, 8 insertions(+), 26 deletions(-)

diff --git a/crates/bevy_animation/Cargo.toml b/crates/bevy_animation/Cargo.toml
index 1614d98f54980..6fb9fb9f5992b 100644
--- a/crates/bevy_animation/Cargo.toml
+++ b/crates/bevy_animation/Cargo.toml
@@ -39,6 +39,7 @@ derive_more = { version = "1", default-features = false, features = [
   "from",
   "display",
 ] }
+either = "1.13"
 thread_local = "1"
 uuid = { version = "1.7", features = ["v4"] }
 smallvec = "1"
diff --git a/crates/bevy_animation/src/gltf_curves.rs b/crates/bevy_animation/src/gltf_curves.rs
index 74d86fd03baf8..8d3b6cc248442 100644
--- a/crates/bevy_animation/src/gltf_curves.rs
+++ b/crates/bevy_animation/src/gltf_curves.rs
@@ -6,6 +6,7 @@ use bevy_math::{
 };
 use bevy_reflect::Reflect;
 use derive_more::derive::{Display, Error, From};
+use either::Either;
 
 /// A keyframe-defined curve that "interpolates" by stepping at `t = 1.0` to the next keyframe.
 #[derive(Debug, Clone, Reflect)]
@@ -189,11 +190,11 @@ where
         match self.core.sample_interp(t) {
             InterpolationDatum::Exact(v)
             | InterpolationDatum::LeftTail(v)
-            | InterpolationDatum::RightTail(v) => TwoIterators::Left(v.iter().copied()),
+            | InterpolationDatum::RightTail(v) => Either::Left(v.iter().copied()),
 
             InterpolationDatum::Between(u, v, s) => {
                 let interpolated = u.iter().zip(v.iter()).map(move |(x, y)| x.lerp(*y, s));
-                TwoIterators::Right(interpolated)
+                Either::Right(interpolated)
             }
         }
     }
@@ -243,14 +244,14 @@ where
         match self.core.sample_interp(t) {
             InterpolationDatum::Exact(v)
             | InterpolationDatum::LeftTail(v)
-            | InterpolationDatum::RightTail(v) => TwoIterators::Left(v.iter().cloned()),
+            | InterpolationDatum::RightTail(v) => Either::Left(v.iter().cloned()),
 
             InterpolationDatum::Between(u, v, s) => {
                 let interpolated =
                     u.iter()
                         .zip(v.iter())
                         .map(move |(x, y)| if s >= 1.0 { y.clone() } else { x.clone() });
-                TwoIterators::Right(interpolated)
+                Either::Right(interpolated)
             }
         }
     }
@@ -302,10 +303,10 @@ where
                 // Pick out the part of this that actually represents the position (instead of tangents),
                 // which is the middle third.
                 let width = self.core.width();
-                TwoIterators::Left(v[width..(width * 2)].iter().copied())
+                Either::Left(v[width..(width * 2)].iter().copied())
             }
 
-            InterpolationDatum::Between((t0, u), (t1, v), s) => TwoIterators::Right(
+            InterpolationDatum::Between((t0, u), (t1, v), s) => Either::Right(
                 cubic_spline_interpolate_slices(self.core.width() / 3, u, v, s, t1 - t0),
             ),
         }
@@ -392,26 +393,6 @@ pub enum WeightsCurve {
 // HELPERS //
 //---------//
 
-enum TwoIterators<A, B> {
-    Left(A),
-    Right(B),
-}
-
-impl<A, B, T> Iterator for TwoIterators<A, B>
-where
-    A: Iterator<Item = T>,
-    B: Iterator<Item = T>,
-{
-    type Item = T;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        match self {
-            TwoIterators::Left(a) => a.next(),
-            TwoIterators::Right(b) => b.next(),
-        }
-    }
-}
-
 /// Helper function for cubic spline interpolation.
 fn cubic_spline_interpolation<T>(
     value_start: T,