Use Generic Associated Types for Enum trait

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       matrix:
         toolchain:
-          - 1.61
+          - "1.65"
           - stable
           - beta
           - nightly

enum-map-derive/src/derive_enum.rs

@@ -37,7 +37,7 @@ impl EnumGenerator {
         quote! {
             #[automatically_derived]
             impl ::enum_map::Enum for #name {
-                const LENGTH: ::enum_map::usize = #length;
+                type Array<V> = [V; #length];
 
                 #[inline]
                 fn from_usize(value: ::enum_map::usize) -> Self {
@@ -53,11 +53,6 @@ impl EnumGenerator {
                     }
                 }
             }
-
-            #[automatically_derived]
-            impl<V> ::enum_map::EnumArray<V> for #name {
-                type Array = [V; #length];
-            }
         }
     }
 

enum-map-derive/src/derive_struct.rs

@@ -102,7 +102,7 @@ impl StructGenerator {
         quote! {
             #[automatically_derived]
             impl ::enum_map::Enum for #name {
-                const LENGTH: ::enum_map::usize = #length;
+                type Array<V> = [V; #length];
 
                 #[inline]
                 fn from_usize(value: ::enum_map::usize) -> Self {
@@ -114,11 +114,6 @@ impl StructGenerator {
                     #into_usize
                 }
             }
-
-            #[automatically_derived]
-            impl<V> ::enum_map::EnumArray<V> for #name {
-                type Array = [V; #length];
-            }
         }
     }
 }

enum-map-derive/src/lib.rs

@@ -165,6 +165,6 @@ pub fn derive_enum_map(input: proc_macro::TokenStream) -> proc_macro::TokenStrea
 
 fn type_length(ty: &Type) -> TokenStream {
     quote! {
-        <#ty as ::enum_map::Enum>::LENGTH
+        ::enum_map::enum_len::<#ty>()
     }
 }

enum-map/Cargo.toml

@@ -3,7 +3,7 @@ name = "enum-map"
 version = "2.6.2"
 authors = ["Konrad Borowski <konrad@borowski.pw>"]
 edition = "2021"
-rust-version = "1.61"
+rust-version = "1.65"
 repository = "https://github.com/xfix/enum-map"
 license = "MIT OR Apache-2.0"
 description = "A map with C-like enum keys represented internally as an array"

enum-map/src/arbitrary.rs

@@ -1,22 +1,24 @@
-use crate::{enum_map, EnumArray, EnumMap};
+use crate::internal::Array;
+use crate::{enum_map, Enum, EnumMap};
 use arbitrary::{Arbitrary, Result, Unstructured};
 
 /// Requires crate feature `"arbitrary"`
-impl<'a, K: EnumArray<V>, V: Arbitrary<'a>> Arbitrary<'a> for EnumMap<K, V> {
+impl<'a, K: Enum, V: Arbitrary<'a>> Arbitrary<'a> for EnumMap<K, V> {
     fn arbitrary(u: &mut Unstructured<'a>) -> Result<EnumMap<K, V>> {
         Ok(enum_map! {
             _ => Arbitrary::arbitrary(u)?,
         })
     }
 
     fn size_hint(depth: usize) -> (usize, Option<usize>) {
-        if K::LENGTH == 0 {
+        let len = K::Array::<V>::LENGTH;
+        if len == 0 {
             (0, Some(0))
         } else {
             let (lo, hi) = V::size_hint(depth);
             (
-                lo.saturating_mul(K::LENGTH),
-                hi.and_then(|hi| hi.checked_mul(K::LENGTH)),
+                lo.saturating_mul(len),
+                hi.and_then(|hi| hi.checked_mul(len)),
             )
         }
     }

enum-map/src/enum_map_impls.rs

@@ -1,16 +1,16 @@
-use crate::{enum_map, EnumArray, EnumMap};
+use crate::{enum_map, Enum, EnumMap};
 use core::fmt::{self, Debug, Formatter};
 use core::hash::{Hash, Hasher};
 use core::iter::{Extend, FromIterator};
 use core::ops::{Index, IndexMut};
 
-impl<K: EnumArray<V> + Debug, V: Debug> Debug for EnumMap<K, V> {
+impl<K: Enum + Debug, V: Debug> Debug for EnumMap<K, V> {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
         f.debug_map().entries(self).finish()
     }
 }
 
-impl<K: EnumArray<V>, V> Extend<(K, V)> for EnumMap<K, V> {
+impl<K: Enum, V> Extend<(K, V)> for EnumMap<K, V> {
     fn extend<I: IntoIterator<Item = (K, V)>>(&mut self, iter: I) {
         for (key, value) in iter {
             self[key] = value;
@@ -20,7 +20,7 @@ impl<K: EnumArray<V>, V> Extend<(K, V)> for EnumMap<K, V> {
 
 impl<'a, K, V> Extend<(&'a K, &'a V)> for EnumMap<K, V>
 where
-    K: EnumArray<V> + Copy,
+    K: Enum + Copy,
     V: Copy,
 {
     fn extend<I: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: I) {
@@ -31,7 +31,7 @@ where
 impl<K, V> FromIterator<(K, V)> for EnumMap<K, V>
 where
     Self: Default,
-    K: EnumArray<V>,
+    K: Enum,
 {
     fn from_iter<I: IntoIterator<Item = (K, V)>>(iter: I) -> Self {
         let mut map = EnumMap::default();
@@ -40,7 +40,7 @@ where
     }
 }
 
-impl<K: EnumArray<V>, V> Index<K> for EnumMap<K, V> {
+impl<K: Enum, V> Index<K> for EnumMap<K, V> {
     type Output = V;
 
     #[inline]
@@ -49,7 +49,7 @@ impl<K: EnumArray<V>, V> Index<K> for EnumMap<K, V> {
     }
 }
 
-impl<K: EnumArray<V>, V> IndexMut<K> for EnumMap<K, V> {
+impl<K: Enum, V> IndexMut<K> for EnumMap<K, V> {
     #[inline]
     fn index_mut(&mut self, key: K) -> &mut V {
         &mut self.as_mut_slice()[key.into_usize()]
@@ -58,9 +58,9 @@ impl<K: EnumArray<V>, V> IndexMut<K> for EnumMap<K, V> {
 
 // Implementations provided by derive attribute are too specific, and put requirements on K.
 // This is caused by rust-lang/rust#26925.
-impl<K: EnumArray<V>, V> Clone for EnumMap<K, V>
+impl<K: Enum, V> Clone for EnumMap<K, V>
 where
-    K::Array: Clone,
+    K::Array<V>: Clone,
 {
     #[inline]
     fn clone(&self) -> Self {
@@ -70,38 +70,38 @@ where
     }
 }
 
-impl<K: EnumArray<V>, V> Copy for EnumMap<K, V> where K::Array: Copy {}
+impl<K: Enum, V> Copy for EnumMap<K, V> where K::Array<V>: Copy {}
 
-impl<K: EnumArray<V>, V: PartialEq> PartialEq for EnumMap<K, V> {
+impl<K: Enum, V: PartialEq> PartialEq for EnumMap<K, V> {
     #[inline]
     fn eq(&self, other: &Self) -> bool {
         self.as_slice() == other.as_slice()
     }
 }
 
-impl<K: EnumArray<V>, V: Eq> Eq for EnumMap<K, V> {}
+impl<K: Enum, V: Eq> Eq for EnumMap<K, V> {}
 
-impl<K: EnumArray<V>, V: Hash> Hash for EnumMap<K, V> {
+impl<K: Enum, V: Hash> Hash for EnumMap<K, V> {
     #[inline]
     fn hash<H: Hasher>(&self, state: &mut H) {
         self.as_slice().hash(state);
     }
 }
 
-impl<K: EnumArray<V>, V: Default> Default for EnumMap<K, V> {
+impl<K: Enum, V: Default> Default for EnumMap<K, V> {
     #[inline]
     fn default() -> Self {
         enum_map! { _ => V::default() }
     }
 }
 
-impl<K: EnumArray<V>, V: PartialOrd> PartialOrd for EnumMap<K, V> {
+impl<K: Enum, V: PartialOrd> PartialOrd for EnumMap<K, V> {
     fn partial_cmp(&self, other: &Self) -> Option<core::cmp::Ordering> {
         self.as_slice().partial_cmp(other.as_slice())
     }
 }
 
-impl<K: EnumArray<V>, V: Ord> Ord for EnumMap<K, V> {
+impl<K: Enum, V: Ord> Ord for EnumMap<K, V> {
     fn cmp(&self, other: &Self) -> core::cmp::Ordering {
         self.as_slice().cmp(other.as_slice())
     }

enum-map/src/internal.rs

@@ -9,39 +9,35 @@ use core::convert::Infallible;
 /// strictly speaking not an actual enum, there are good reasons to consider
 /// it like one, as array of `u8` keys is a relatively common pattern.
 pub trait Enum: Sized {
-    /// Length of the enum.
-    const LENGTH: usize;
+    /// Representation of an enum.
+    ///
+    /// For an enum with four elements it looks like this.
+    ///
+    /// ```
+    /// type Array<V> = [V; 4];
+    /// ```
+    type Array<V>: Array;
 
     /// Takes an usize, and returns an element matching `into_usize` function.
     fn from_usize(value: usize) -> Self;
     /// Returns an unique identifier for a value within range of `0..Array::LENGTH`.
     fn into_usize(self) -> usize;
 }
 
-/// Trait associating enum with an array.
-///
-/// This exists due to limitations of Rust compiler that prevent arrays from using
-/// associated constants in structures. The array length must match `LENGTH` of an
-/// `Enum`.
-pub trait EnumArray<V>: Enum {
-    /// Representation of an enum map for type `V`.
-    type Array: Array<V>;
-}
-
 /// Array for enum-map storage.
 ///
 /// This trait is inteded for primitive array types (with fixed length).
 ///
 /// # Safety
 ///
 /// The array length needs to match actual storage.
-pub unsafe trait Array<V> {
+pub unsafe trait Array {
     // This is necessary duplication because the length in Enum trait can be
     // provided by user and may not be trustworthy for unsafe code.
     const LENGTH: usize;
 }
 
-unsafe impl<V, const N: usize> Array<V> for [V; N] {
+unsafe impl<V, const N: usize> Array for [V; N] {
     const LENGTH: usize = N;
 }
 
@@ -52,7 +48,7 @@ pub fn out_of_bounds() -> ! {
 }
 
 impl Enum for bool {
-    const LENGTH: usize = 2;
+    type Array<V> = [V; 2];
 
     #[inline]
     fn from_usize(value: usize) -> Self {
@@ -68,12 +64,8 @@ impl Enum for bool {
     }
 }
 
-impl<T> EnumArray<T> for bool {
-    type Array = [T; Self::LENGTH];
-}
-
 impl Enum for () {
-    const LENGTH: usize = 1;
+    type Array<V> = [V; 1];
 
     #[inline]
     fn from_usize(value: usize) -> Self {
@@ -88,12 +80,8 @@ impl Enum for () {
     }
 }
 
-impl<T> EnumArray<T> for () {
-    type Array = [T; Self::LENGTH];
-}
-
 impl Enum for u8 {
-    const LENGTH: usize = 256;
+    type Array<V> = [V; 256];
 
     #[inline]
     fn from_usize(value: usize) -> Self {
@@ -105,12 +93,8 @@ impl Enum for u8 {
     }
 }
 
-impl<T> EnumArray<T> for u8 {
-    type Array = [T; Self::LENGTH];
-}
-
 impl Enum for Infallible {
-    const LENGTH: usize = 0;
+    type Array<V> = [V; 0];
 
     #[inline]
     fn from_usize(_: usize) -> Self {
@@ -122,12 +106,8 @@ impl Enum for Infallible {
     }
 }
 
-impl<T> EnumArray<T> for Infallible {
-    type Array = [T; Self::LENGTH];
-}
-
 impl Enum for Ordering {
-    const LENGTH: usize = 3;
+    type Array<V> = [V; 3];
 
     #[inline]
     fn from_usize(value: usize) -> Self {
@@ -147,7 +127,3 @@ impl Enum for Ordering {
         }
     }
 }
-
-impl<T> EnumArray<T> for Ordering {
-    type Array = [T; Self::LENGTH];
-}