std::util: Modernize NonCopyable constructor

part of #3853

Author: Blei

src/libstd/option.rs

@@ -437,7 +437,7 @@ fn test_option_dance() {
 }
 #[test] #[should_fail] #[ignore(cfg(windows))]
 fn test_option_too_much_dance() {
-    let mut y = Some(util::NonCopyable());
+    let mut y = Some(util::NonCopyable::new());
     let _y2 = y.swap_unwrap();
     let _y3 = y.swap_unwrap();
 }

src/libstd/util.rs

@@ -79,13 +79,15 @@ pub struct NonCopyable {
     priv i: (),
 }
 
+impl NonCopyable {
+    /// Creates a dummy non-copyable structure and returns it for use.
+    pub fn new() -> NonCopyable { NonCopyable { i: () } }
+}
+
 impl Drop for NonCopyable {
     fn finalize(&self) { }
 }
 
-/// Creates a dummy non-copyable structure and returns it for use.
-pub fn NonCopyable() -> NonCopyable { NonCopyable { i: () } }
-
 
 /// A type with no inhabitants
 pub enum Void { }