From fc5d6143d34ae6c691da147a5a378d8db5d8c943 Mon Sep 17 00:00:00 2001
From: Tony Arcieri <bascule@gmail.com>
Date: Sat, 30 Dec 2023 17:21:56 -0700
Subject: [PATCH] Impl `From<Array<T, U>>` for `[T; N]` generically (#1010)

Uses a const generic implementation bounded on `ArrayOps<T, N>` rather
than using a macro to write a separate one for each array size.
---
 hybrid-array/src/impls.rs |  6 ------
 hybrid-array/src/lib.rs   | 15 ++++++++++++++-
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/hybrid-array/src/impls.rs b/hybrid-array/src/impls.rs
index 76cf70b0..55542ffc 100644
--- a/hybrid-array/src/impls.rs
+++ b/hybrid-array/src/impls.rs
@@ -75,12 +75,6 @@ macro_rules! impl_array_size {
             impl<T> AssociatedArraySize for Array<T, typenum::$ty> {
                 type Size = typenum::$ty;
             }
-
-            impl<T> From<Array<T, typenum::$ty>> for [T; $len] {
-                fn from(arr: Array<T, typenum::$ty>) -> [T; $len] {
-                    arr.0
-                }
-            }
         )+
      };
 }
diff --git a/hybrid-array/src/lib.rs b/hybrid-array/src/lib.rs
index 66602ee7..a9462485 100644
--- a/hybrid-array/src/lib.rs
+++ b/hybrid-array/src/lib.rs
@@ -348,6 +348,18 @@ where
     }
 }
 
+impl<T, U, const N: usize> From<Array<T, U>> for [T; N]
+where
+    Array<T, U>: ArrayOps<T, N>,
+    U: ArraySize,
+{
+    #[inline]
+    fn from(arr: Array<T, U>) -> [T; N] {
+        let mut items = arr.0.into_iter();
+        core::array::from_fn(|_| items.next().expect("should always have item"))
+    }
+}
+
 impl<'a, T, U, const N: usize> From<&'a [T; N]> for &'a Array<T, U>
 where
     Array<T, U>: ArrayOps<T, N>,
@@ -543,6 +555,7 @@ pub trait ArrayOps<T, const N: usize>:
     + Borrow<[T; N]>
     + BorrowMut<[T; N]>
     + From<[T; N]>
+    + FromFn<T>
     + Into<[T; N]>
     + IntoIterator<Item = T>
     + Sized
@@ -616,8 +629,8 @@ impl<T, U: ArraySize> SliceOps<T> for Array<T, U> {}
 pub unsafe trait ArraySize: Unsigned {
     /// Array type which corresponds to this size.
     type ArrayType<T>: AssociatedArraySize<Size = Self>
-        + FromFn<T>
         + From<Array<T, Self>>
+        + FromFn<T>
         + Into<Array<T, Self>>
         + IntoIterator<Item = T>
         + SliceOps<T>;