string-wrapper: add Copy, Default, and is_empty

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "string-wrapper"
-version = "0.1.1"
+version = "0.1.2"
 authors = ["Simon Sapin <simon.sapin@exyr.org>"]
 license = "MIT"
 repository = "https://github.com/SimonSapin/rust-std-candidates"

lib.rs

@@ -8,7 +8,7 @@ use std::str;
 /// Like `String`, but with a fixed capacity and a generic backing bytes storage.
 ///
 /// Use e.g. `StringWrapper<[u8; 4]>` to have a string without heap memory allocation.
-#[derive(Clone)]
+#[derive(Clone, Copy, Default)]
 pub struct StringWrapper<T> where T: Buffer {
     len: usize,
     buffer: T,
@@ -60,6 +60,10 @@ impl<T> StringWrapper<T> where T: Buffer {
         self.len
     }
 
+    pub fn is_empty(&self) -> bool {
+        self.len == 0
+    }
+
     /// Users must ensure that the string remains well-formed UTF-8.
     pub unsafe fn set_len(&mut self, new_len: usize) {
         self.len = new_len