Miscellaneous small changes (#1238)

* Use a slice instead of a new object

* Remove unnecessary 'into_iter'

* Use 'and_then' instead of 'map_or'

src/platform_impl/macos/event.rs

@@ -208,7 +208,7 @@ pub fn scancode_to_keycode(scancode: c_ushort) -> Option<VirtualKeyCode> {
 // While F1-F20 have scancodes we can match on, we have to check against UTF-16
 // constants for the rest.
 // https://developer.apple.com/documentation/appkit/1535851-function-key_unicodes?preferredLanguage=occ
-pub fn check_function_keys(string: &String) -> Option<VirtualKeyCode> {
+pub fn check_function_keys(string: &str) -> Option<VirtualKeyCode> {
     if let Some(ch) = string.encode_utf16().next() {
         return Some(match ch {
             0xf718 => VirtualKeyCode::F21,

src/platform_impl/macos/monitor.rs

@@ -248,7 +248,6 @@ impl MonitorHandle {
                 assert!(!array.is_null(), "failed to get list of display modes");
                 let array_count = CFArrayGetCount(array);
                 let modes: Vec<_> = (0..array_count)
-                    .into_iter()
                     .map(move |i| {
                         let mode = CFArrayGetValueAtIndex(array, i) as *mut _;
                         ffi::CGDisplayModeRetain(mode);

src/platform_impl/macos/view.rs

@@ -520,10 +520,7 @@ fn retrieve_keycode(event: id) -> Option<VirtualKeyCode> {
     #[inline]
     fn get_code(ev: id, raw: bool) -> Option<VirtualKeyCode> {
         let characters = get_characters(ev, raw);
-        characters
+        characters.chars().next().and_then(|c| char_to_keycode(c))
-            .chars()
-            .next()
-            .map_or(None, |c| char_to_keycode(c))
     }
 
     // Cmd switches Roman letters for Dvorak-QWERTY layout, so we try modified characters first.