Add Extensions::extend (#546)

CHANGELOG.md

@@ -1,3 +1,7 @@
+# Unreleased
+
+* Add `extend()` method to `Extension`.
+
 # 0.2.6 (December 30, 2021)
 
 * Upgrade internal `itoa` dependency to 1.0.

src/extensions.rs

@@ -188,6 +188,39 @@ impl Extensions {
             .as_ref()
             .map_or(0, |map| map.len())
     }
+
+    /// Extends `self` with another `Extensions`.
+    ///
+    /// If an instance of a specific type exists in both, the one in `self` is overwritten with the
+    /// one from `other`.
+    /// 
+    /// # Example
+    /// 
+    /// ```
+    /// # use http::Extensions;
+    /// let mut ext_a = Extensions::new();
+    /// ext_a.insert(8u8);
+    /// ext_a.insert(16u16);
+    /// 
+    /// let mut ext_b = Extensions::new();
+    /// ext_b.insert(4u8);
+    /// ext_b.insert("hello");
+    /// 
+    /// ext_a.extend(ext_b);
+    /// assert_eq!(ext_a.len(), 3);
+    /// assert_eq!(ext_a.get::<u8>(), Some(&4u8));
+    /// assert_eq!(ext_a.get::<u16>(), Some(&16u16));
+    /// assert_eq!(ext_a.get::<&'static str>().copied(), Some("hello"));
+    /// ```
+    pub fn extend(&mut self, other: Self) {
+        if let Some(other) = other.map {
+            if let Some(map) = &mut self.map {
+                map.extend(*other);
+            } else {
+                self.map = Some(other);
+            }
+        }
+    }
 }
 
 impl fmt::Debug for Extensions {