Merge pull request #1149 from joshka/master

Add Map::shift_insert()

Author: dtolnay

src/map.rs

@@ -127,6 +127,17 @@ impl Map<String, Value> {
         self.map.insert(k, v)
     }
 
+    /// Insert a key-value pair in the map at the given index.
+    ///
+    /// If the map did not have this key present, `None` is returned.
+    ///
+    /// If the map did have this key present, the key is moved to the new
+    /// position, the value is updated, and the old value is returned.
+    #[cfg(feature = "preserve_order")]
+    pub fn shift_insert(&mut self, index: usize, k: String, v: Value) -> Option<Value> {
+        self.map.shift_insert(index, k, v)
+    }
+
     /// Removes a key from the map, returning the value at the key if the key
     /// was previously in the map.
     ///

tests/map.rs

@@ -15,6 +15,17 @@ fn test_preserve_order() {
     assert_eq!(keys, EXPECTED);
 }
 
+#[test]
+#[cfg(feature = "preserve_order")]
+fn test_shift_insert() {
+    let mut v: Value = from_str(r#"{"b":null,"a":null,"c":null}"#).unwrap();
+    let val = v.as_object_mut().unwrap();
+    val.shift_insert(0, "d".to_string(), Value::Null);
+
+    let keys: Vec<_> = val.keys().collect();
+    assert_eq!(keys, &["d", "b", "a", "c"]);
+}
+
 #[test]
 fn test_append() {
     // Sorted order