Add Rope::delete_at_char_index()

src/core/rope.rs

@@ -101,7 +101,11 @@ impl Rope {
     }
 
     /// Insert new text into the rope at a given character index.
-    pub fn insert_at_char_index(self: &Rc<Rope>, index: usize, text: impl Into<String>) -> Rc<Rope> {
+    pub fn insert_at_char_index(
+        self: &Rc<Rope>,
+        index: usize,
+        text: impl Into<String>,
+    ) -> Rc<Rope> {
         let new_node = Rope::new(text);
         let total_chars = self.total_chars();
         if index == 0 {
@@ -116,6 +120,13 @@ impl Rope {
         }
     }
 
+    /// Return a new rope with `length` characters removed after `start`.
+    pub fn delete_at_char_index(self: &Rc<Rope>, start: usize, length: usize) -> Rc<Rope> {
+        let (beginning, rest) = self.split_at_char_index(start);
+        let (_, end) = rest.split_at_char_index(length);
+        beginning.concat(end)
+    }
+
     /// Split the rope in two at character `index`.
     ///
     /// The result is two Ropes—one containing the first 'i' characters of the
@@ -554,8 +565,29 @@ mod tests {
         let rope2 = rope1.insert_at_char_index(9, " ");
         assert_eq!(target.iter_chars().collect::<String>(), "The brown dog");
         assert_eq!(rope1.iter_chars().collect::<String>(), "The quickbrown dog");
-        assert_eq!(rope2.iter_chars().collect::<String>(), "The quick brown dog");
-        let rope3 = rope2.insert_at_char_index("The quick brown dog".len(), " jumps over the lazy fox.");
-        assert_eq!(rope3.iter_chars().collect::<String>(), "The quick brown dog jumps over the lazy fox.");
+        assert_eq!(
+            rope2.iter_chars().collect::<String>(),
+            "The quick brown dog"
+        );
+        let rope3 =
+            rope2.insert_at_char_index("The quick brown dog".len(), " jumps over the lazy fox.");
+        assert_eq!(
+            rope3.iter_chars().collect::<String>(),
+            "The quick brown dog jumps over the lazy fox."
+        );
+    }
+
+    #[test]
+    fn delete_at_char_index() {
+        let target = Rope::new("The quick brown fox jumps over the lazy dog.");
+        let test = target.delete_at_char_index(10, 6);
+        assert_eq!(target.iter_chars().collect::<String>(), "The quick brown fox jumps over the lazy dog.");
+        assert_eq!(test.iter_chars().collect::<String>(), "The quick fox jumps over the lazy dog.");
+        let test = target.delete_at_char_index(0, 4);
+        assert_eq!(target.iter_chars().collect::<String>(), "The quick brown fox jumps over the lazy dog.");
+        assert_eq!(test.iter_chars().collect::<String>(), "quick brown fox jumps over the lazy dog.");
+        let test = target.delete_at_char_index("The quick brown fox jumps over the lazy dog.".len()-5, 5);
+        assert_eq!(target.iter_chars().collect::<String>(), "The quick brown fox jumps over the lazy dog.");
+        assert_eq!(test.iter_chars().collect::<String>(), "The quick brown fox jumps over the lazy");
     }
 }