str/slice: factor out overflow error messages

Author: ExpHP

src/libcore/slice/mod.rs

@@ -2262,6 +2262,12 @@ fn slice_index_order_fail(index: usize, end: usize) -> ! {
     panic!("slice index starts at {} but ends at {}", index, end);
 }
 
+#[inline(never)]
+#[cold]
+fn slice_index_overflow_fail() -> ! {
+    panic!("attempted to index slice up to maximum usize");
+}
+
 /// A helper trait used for indexing operations.
 #[unstable(feature = "slice_get_slice", issue = "35729")]
 #[rustc_on_unimplemented = "slice indices are of type `usize` or ranges of `usize`"]
@@ -2538,15 +2544,13 @@ impl<T> SliceIndex<[T]> for ops::RangeInclusive<usize> {
 
     #[inline]
     fn index(self, slice: &[T]) -> &[T] {
-        assert!(self.end != usize::max_value(),
-            "attempted to index slice up to maximum usize");
+        if self.end == usize::max_value() { slice_index_overflow_fail(); }
         (self.start..self.end + 1).index(slice)
     }
 
     #[inline]
     fn index_mut(self, slice: &mut [T]) -> &mut [T] {
-        assert!(self.end != usize::max_value(),
-            "attempted to index slice up to maximum usize");
+        if self.end == usize::max_value() { slice_index_overflow_fail(); }
         (self.start..self.end + 1).index_mut(slice)
     }
 }

src/libcore/str/mod.rs

@@ -1849,6 +1849,12 @@ mod traits {
         }
     }
 
+    #[inline(never)]
+    #[cold]
+    fn str_index_overflow_fail() -> ! {
+        panic!("attempted to index str up to maximum usize");
+    }
+
     #[stable(feature = "str_checked_slicing", since = "1.20.0")]
     impl SliceIndex<str> for ops::RangeFull {
         type Output = str;
@@ -2053,14 +2059,12 @@ mod traits {
         }
         #[inline]
         fn index(self, slice: &str) -> &Self::Output {
-            assert!(self.end != usize::max_value(),
-                "attempted to index str up to maximum usize");
+            if self.end == usize::max_value() { str_index_overflow_fail(); }
             (self.start..self.end+1).index(slice)
         }
         #[inline]
         fn index_mut(self, slice: &mut str) -> &mut Self::Output {
-            assert!(self.end != usize::max_value(),
-                "attempted to index str up to maximum usize");
+            if self.end == usize::max_value() { str_index_overflow_fail(); }
             (self.start..self.end+1).index_mut(slice)
         }
     }
@@ -2098,14 +2102,12 @@ mod traits {
         }
         #[inline]
         fn index(self, slice: &str) -> &Self::Output {
-            assert!(self.end != usize::max_value(),
-                "attempted to index str up to maximum usize");
+            if self.end == usize::max_value() { str_index_overflow_fail(); }
             (..self.end+1).index(slice)
         }
         #[inline]
         fn index_mut(self, slice: &mut str) -> &mut Self::Output {
-            assert!(self.end != usize::max_value(),
-                "attempted to index str up to maximum usize");
+            if self.end == usize::max_value() { str_index_overflow_fail(); }
             (..self.end+1).index_mut(slice)
         }
     }