add UnwrapNever helper to remove some unsafe

src/basic.rs

@@ -13,7 +13,7 @@ use core::marker::PhantomData;
 use core::mem::{ManuallyDrop, MaybeUninit};
 use core::ops::{Index, IndexMut};
 
-use crate::util::{Never, UnwrapUnchecked};
+use crate::util::{Never, UnwrapNever};
 use crate::{DefaultKey, Key, KeyData};
 
 // Storage inside a slot or metadata for the freelist when vacant.
@@ -344,7 +344,8 @@ impl<K: Key, V> SlotMap<K, V> {
     /// ```
     #[inline(always)]
     pub fn insert(&mut self, value: V) -> K {
-        unsafe { self.try_insert_with_key::<_, Never>(move |_| Ok(value)).unwrap_unchecked_() }
+        self.try_insert_with_key::<_, Never>(move |_| Ok(value))
+            .unwrap_never()
     }
 
     /// Inserts a value given by `f` into the slot map. The key where the
@@ -369,7 +370,8 @@ impl<K: Key, V> SlotMap<K, V> {
     where
         F: FnOnce(K) -> V,
     {
-        unsafe { self.try_insert_with_key::<_, Never>(move |k| Ok(f(k))).unwrap_unchecked_() }
+        self.try_insert_with_key::<_, Never>(move |k| Ok(f(k)))
+            .unwrap_never()
     }
 
     /// Inserts a value given by `f` into the slot map. The key where the

src/dense.rs

@@ -14,7 +14,7 @@ use core::iter::FusedIterator;
 use core::mem::MaybeUninit;
 use core::ops::{Index, IndexMut};
 
-use crate::util::{Never, UnwrapUnchecked};
+use crate::util::{Never, UnwrapNever};
 use crate::{DefaultKey, Key, KeyData};
 
 // A slot, which represents storage for an index and a current version.
@@ -252,7 +252,8 @@ impl<K: Key, V> DenseSlotMap<K, V> {
     /// ```
     #[inline(always)]
     pub fn insert(&mut self, value: V) -> K {
-        unsafe { self.try_insert_with_key::<_, Never>(move |_| Ok(value)).unwrap_unchecked_() }
+        self.try_insert_with_key::<_, Never>(move |_| Ok(value))
+            .unwrap_never()
     }
 
     /// Inserts a value given by `f` into the slot map. The key where the
@@ -277,7 +278,8 @@ impl<K: Key, V> DenseSlotMap<K, V> {
     where
         F: FnOnce(K) -> V,
     {
-        unsafe { self.try_insert_with_key::<_, Never>(move |k| Ok(f(k))).unwrap_unchecked_() }
+        self.try_insert_with_key::<_, Never>(move |k| Ok(f(k)))
+            .unwrap_never()
     }
 
     /// Inserts a value given by `f` into the slot map. The key where the

src/hop.rs

@@ -25,7 +25,7 @@ use core::mem::ManuallyDrop;
 use core::mem::MaybeUninit;
 use core::ops::{Index, IndexMut};
 
-use crate::util::{Never, UnwrapUnchecked};
+use crate::util::{Never, UnwrapNever};
 use crate::{DefaultKey, Key, KeyData};
 
 // Metadata to maintain the freelist.
@@ -363,7 +363,8 @@ impl<K: Key, V> HopSlotMap<K, V> {
     /// ```
     #[inline(always)]
     pub fn insert(&mut self, value: V) -> K {
-        unsafe { self.try_insert_with_key::<_, Never>(move |_| Ok(value)).unwrap_unchecked_() }
+        self.try_insert_with_key::<_, Never>(move |_| Ok(value))
+            .unwrap_never()
     }
 
     // Helper function to make using the freelist painless.
@@ -395,7 +396,8 @@ impl<K: Key, V> HopSlotMap<K, V> {
     where
         F: FnOnce(K) -> V,
     {
-        unsafe { self.try_insert_with_key::<_, Never>(move |k| Ok(f(k))).unwrap_unchecked_() }
+        self.try_insert_with_key::<_, Never>(move |k| Ok(f(k)))
+            .unwrap_never()
     }
 
     /// Inserts a value given by `f` into the slot map. The key where the

src/util.rs

@@ -32,15 +32,15 @@ impl<T> UnwrapUnchecked<T> for Option<T> {
     }
 }
 
-impl<T, E: Debug> UnwrapUnchecked<T> for Result<T, E> {
-    unsafe fn unwrap_unchecked_(self) -> T {
-        if cfg!(debug_assertions) {
-            self.unwrap()
-        } else {
-            match self {
-                Ok(x) => x,
-                Err(_) => unreachable_unchecked(),
-            }
+pub trait UnwrapNever<T> {
+    fn unwrap_never(self) -> T;
+}
+
+impl<T> UnwrapNever<T> for Result<T, Never> {
+    fn unwrap_never(self) -> T {
+        match self {
+            Ok(t) => t,
+            Err(e) => match e {},
         }
     }
 }