ctutils: replace [T]: ... bounds with T: *Slice (#1395)

This should make it clearer to users which traits their types need to
impl to be valid for the bounds, rather than indirectly relying on the
blanket impl of `*Slice` traits for `[T]`.

Author: tarcieri

ctutils/src/traits/ct_assign.rs

@@ -123,15 +123,15 @@ impl_ct_assign_with_ct_select!(
 
 impl<T, const N: usize> CtAssign for [T; N]
 where
-    [T]: CtAssign,
+    T: CtAssignSlice,
 {
     #[inline]
     fn ct_assign(&mut self, rhs: &Self, choice: Choice) {
         self.as_mut_slice().ct_assign(rhs, choice);
     }
 }
 
-impl<T, const N: usize> CtAssignSlice for [T; N] where [T]: CtAssign {}
+impl<T, const N: usize> CtAssignSlice for [T; N] where T: CtAssignSlice {}
 
 #[cfg(feature = "subtle")]
 impl CtAssign for subtle::Choice {
@@ -154,7 +154,7 @@ where
 }
 #[cfg(feature = "alloc")]
 mod alloc {
-    use super::{Choice, CtAssign};
+    use super::{Choice, CtAssign, CtAssignSlice};
     use ::alloc::{boxed::Box, vec::Vec};
 
     impl<T> CtAssign for Box<T>
@@ -170,7 +170,7 @@ mod alloc {
 
     impl<T> CtAssign for Box<[T]>
     where
-        [T]: CtAssign,
+        T: CtAssignSlice,
     {
         #[inline]
         #[track_caller]
@@ -181,7 +181,7 @@ mod alloc {
 
     impl<T> CtAssign<[T]> for Box<[T]>
     where
-        [T]: CtAssign,
+        T: CtAssignSlice,
     {
         #[inline]
         #[track_caller]
@@ -192,7 +192,7 @@ mod alloc {
 
     impl<T> CtAssign for Vec<T>
     where
-        [T]: CtAssign,
+        T: CtAssignSlice,
     {
         #[inline]
         #[track_caller]
@@ -203,7 +203,7 @@ mod alloc {
 
     impl<T> CtAssign<[T]> for Vec<T>
     where
-        [T]: CtAssign,
+        T: CtAssignSlice,
     {
         #[inline]
         #[track_caller]

ctutils/src/traits/ct_eq.rs

@@ -152,15 +152,15 @@ impl CtEqSlice for cmp::Ordering {}
 
 impl<T, const N: usize> CtEq for [T; N]
 where
-    [T]: CtEq,
+    T: CtEqSlice,
 {
     #[inline]
     fn ct_eq(&self, other: &[T; N]) -> Choice {
         self.as_slice().ct_eq(other.as_slice())
     }
 }
 
-impl<T, const N: usize> CtEqSlice for [T; N] where [T]: CtEq {}
+impl<T, const N: usize> CtEqSlice for [T; N] where T: CtEqSlice {}
 
 #[cfg(feature = "subtle")]
 impl CtEq for subtle::Choice {
@@ -183,7 +183,7 @@ where
 
 #[cfg(feature = "alloc")]
 mod alloc {
-    use super::{Choice, CtEq};
+    use super::{Choice, CtEq, CtEqSlice};
     use ::alloc::{boxed::Box, vec::Vec};
 
     impl<T> CtEq for Box<T>
@@ -199,7 +199,7 @@ mod alloc {
 
     impl<T> CtEq for Box<[T]>
     where
-        [T]: CtEq,
+        T: CtEqSlice,
     {
         #[inline]
         #[track_caller]
@@ -210,7 +210,7 @@ mod alloc {
 
     impl<T> CtEq<[T]> for Box<[T]>
     where
-        [T]: CtEq,
+        T: CtEqSlice,
     {
         #[inline]
         #[track_caller]
@@ -221,7 +221,7 @@ mod alloc {
 
     impl<T> CtEq for Vec<T>
     where
-        [T]: CtEq,
+        T: CtEqSlice,
     {
         #[inline]
         #[track_caller]
@@ -232,7 +232,7 @@ mod alloc {
 
     impl<T> CtEq<[T]> for Vec<T>
     where
-        [T]: CtEq,
+        T: CtEqSlice,
     {
         #[inline]
         #[track_caller]

ctutils/src/traits/ct_select.rs

@@ -1,4 +1,4 @@
-use crate::{Choice, CtAssign};
+use crate::{Choice, CtAssign, CtAssignSlice};
 use core::{
     cmp,
     num::{
@@ -63,8 +63,7 @@ where
 
 impl<T, const N: usize> CtSelectArray<N> for T
 where
-    T: Clone + CtSelect,
-    [T]: CtAssign,
+    T: Clone + CtAssignSlice + CtSelect,
 {
     #[inline]
     fn ct_select_array(a: &[Self; N], b: &[Self; N], choice: Choice) -> [Self; N] {
@@ -181,12 +180,7 @@ mod alloc {
     impl<T: Clone + CtAssign> CtSelectUsingCtAssign for Box<T> {}
 
     #[cfg(feature = "alloc")]
-    impl<T> CtSelectUsingCtAssign for Box<[T]>
-    where
-        T: Clone,
-        [T]: CtAssign,
-    {
-    }
+    impl<T> CtSelectUsingCtAssign for Box<[T]> where T: Clone + CtAssignSlice {}
 
     #[cfg(feature = "alloc")]
     impl<T: Clone + CtAssignSlice> CtSelectUsingCtAssign for Vec<T> {}