fix: try perf

src/with_indices.rs

@@ -35,7 +35,6 @@ where
     }
 
     let line_len = self.line.len();
-
     let mut start_byte_index =
       if start_char_index == 0 { Some(0) } else { None };
     let mut end_byte_index = if end_char_index == usize::MAX {
@@ -52,7 +51,14 @@ where
     if start_char_index >= last_char_index as usize
       || end_char_index >= last_char_index as usize
     {
-      for char in self.line.byte_slice(byte_index..line_len).chars() {
+      #[allow(unsafe_code)]
+      let slice = unsafe {
+        // SAFETY: Since `indices` iterates over the `CharIndices` of `self`, we can guarantee
+        // that the indices obtained from it will always be within the bounds of `self` and they
+        // will always lie on UTF-8 sequence boundaries.
+        self.line.byte_slice_unchecked(byte_index..line_len)
+      };
+      for char in slice.chars() {
         if start_byte_index.is_some() && end_byte_index.is_some() {
           break;
         }
@@ -70,7 +76,14 @@ where
         char_index += 1;
       }
     } else {
-      for char in self.line.byte_slice(0..byte_index).chars().rev() {
+      #[allow(unsafe_code)]
+      let slice = unsafe {
+        // SAFETY: Since `indices` iterates over the `CharIndices` of `self`, we can guarantee
+        // that the indices obtained from it will always be within the bounds of `self` and they
+        // will always lie on UTF-8 sequence boundaries.
+        self.line.byte_slice_unchecked(0..byte_index)
+      };
+      for char in slice.chars().rev() {
         if start_byte_index.is_some() && end_byte_index.is_some() {
           break;
         }