Update arrayvec.rs

src/arrayvec.rs

@@ -1025,16 +1025,15 @@ where
 }
 
 #[cfg(feature = "experimental_write_impl")]
-impl<A> core::fmt::Write for ArrayVec<A>
-where
-  A: Array,
-  A::Item: From<u8>,
+impl<A: Array<Item=u8>> core::fmt::Write for ArrayVec<A>
 {
   fn write_str(&mut self, s: &str) -> core::fmt::Result {
-    if self.len() + s.as_bytes().len() <= A::CAPACITY {
-      for byte in s.bytes() {
-        self.push(A::Item::from(byte))
-      }
+    let my_len = self.len();
+    let str_len = s.as_bytes().len();
+    if my_len + str_len <= A::CAPACITY {
+      let remainder = &mut self.data.as_slice()[my_len..];
+      let target = &mut remainder[..str_len];
+      target.copy_from_slice(s.as_bytes());
       Ok(())
     } else {
       Err(core::fmt::Error)