From 63ba0eb91a9de123c9bd5a58dab5c802320afe03 Mon Sep 17 00:00:00 2001
From: Tony Arcieri <bascule@gmail.com>
Date: Sat, 30 Dec 2023 16:05:23 -0700
Subject: [PATCH] hybrid-array: `AssociatedArraySize` trait (#1006)

Adds a type for associating a `typenum`-based size with a given array
type, which can be either `[T; N]` or `Array<T, U>`.

This subsumes the previous `IntoArray` trait, which can be replaced by a
simple `Into` bound instead.
---
 hybrid-array/src/impls.rs | 20 +++++++++-----------
 hybrid-array/src/lib.rs   | 21 +++++++--------------
 2 files changed, 16 insertions(+), 25 deletions(-)

diff --git a/hybrid-array/src/impls.rs b/hybrid-array/src/impls.rs
index dfe564fb..76cf70b0 100644
--- a/hybrid-array/src/impls.rs
+++ b/hybrid-array/src/impls.rs
@@ -1,4 +1,4 @@
-use super::{Array, ArrayOps, ArraySize, IntoArray};
+use super::{Array, ArrayOps, ArraySize, AssociatedArraySize};
 
 #[cfg(feature = "zeroize")]
 use zeroize::{Zeroize, ZeroizeOnDrop};
@@ -27,7 +27,6 @@ macro_rules! impl_array_size {
         $(
             impl<T> ArrayOps<T, $len> for Array<T, typenum::$ty> {
                 const SIZE: usize = $len;
-                type Size = typenum::$ty;
 
                 #[inline]
                 fn as_core_array(&self) -> &[T; $len] {
@@ -69,17 +68,17 @@ macro_rules! impl_array_size {
                 type ArrayType<T> = [T; $len];
             }
 
-            impl<T> From<Array<T, typenum::$ty>> for [T; $len] {
-                fn from(arr: Array<T, typenum::$ty>) -> [T; $len] {
-                    arr.0
-                }
+            impl<T> AssociatedArraySize for [T; $len] {
+                type Size = typenum::$ty;
             }
 
-            impl<T> IntoArray<T> for [T; $len] {
+            impl<T> AssociatedArraySize for Array<T, typenum::$ty> {
                 type Size = typenum::$ty;
+            }
 
-                fn into_hybrid_array(self) -> Array<T, Self::Size> {
-                    Array::from_core_array(self)
+            impl<T> From<Array<T, typenum::$ty>> for [T; $len] {
+                fn from(arr: Array<T, typenum::$ty>) -> [T; $len] {
+                    arr.0
                 }
             }
         )+
@@ -169,10 +168,9 @@ impl_array_size! {
 
 impl<T, const N: usize> ArrayOps<T, N> for [T; N]
 where
-    Self: IntoArray<T>,
+    Self: AssociatedArraySize,
 {
     const SIZE: usize = N;
-    type Size = <Self as IntoArray<T>>::Size;
 
     #[inline]
     fn as_core_array(&self) -> &[T; N] {
diff --git a/hybrid-array/src/lib.rs b/hybrid-array/src/lib.rs
index 1293a8b3..d41656e6 100644
--- a/hybrid-array/src/lib.rs
+++ b/hybrid-array/src/lib.rs
@@ -536,7 +536,8 @@ fn check_slice_length<T, U: ArraySize>(slice: &[T]) -> Result<(), TryFromSliceEr
 
 /// Array operations which are const generic over a given array size.
 pub trait ArrayOps<T, const N: usize>:
-    Borrow<[T; N]>
+    AssociatedArraySize
+    + Borrow<[T; N]>
     + BorrowMut<[T; N]>
     + From<[T; N]>
     + Into<[T; N]>
@@ -546,14 +547,9 @@ pub trait ArrayOps<T, const N: usize>:
 {
     /// Size of an array as a `usize`.
     ///
-    /// Not to be confused with [`ArrayOps::Size`], which is `typenum`-based.
+    /// Not to be confused with [`AssociatedArraySize::Size`], which is [`typenum`]-based.
     const SIZE: usize;
 
-    /// [`ArraySize`] type: `typenum`-provided [`Unsigned`] integer.
-    ///
-    /// Not to be confused with [`ArrayOps::SIZE`], which is a `usize`.
-    type Size: ArraySize;
-
     /// Returns a reference to the inner array.
     fn as_core_array(&self) -> &[T; N];
 
@@ -652,16 +648,13 @@ impl<T, const N: usize> ArrayExt<T> for [T; N] {
 /// It is implemented only for a number of types defined in [`typenum::consts`].
 pub unsafe trait ArraySize: Unsigned {
     /// Array type which corresponds to this size.
-    type ArrayType<T>: ArrayExt<T> + IntoArray<T> + IntoIterator<Item = T> + SliceOps<T>;
+    type ArrayType<T>: ArrayExt<T> + Into<Array<T, Self>> + IntoIterator<Item = T> + SliceOps<T>;
 }
 
-/// Convert the given type into an [`Array`].
-pub trait IntoArray<T> {
-    /// Size of the [`Array`].
+/// Associates an [`ArraySize`] with a given type.
+pub trait AssociatedArraySize: Sized {
+    /// Size of an array type, expressed as a [`typenum`]-based [`ArraySize`].
     type Size: ArraySize;
-
-    /// Convert into the `hybrid-array` crate's [`Array`] type.
-    fn into_hybrid_array(self) -> Array<T, Self::Size>;
 }
 
 /// Splits the shared slice into a slice of `N`-element arrays, starting at the beginning