FIX: Remove use of uninitialized in ArrayString

We can't fix this properly (MaybeUninit with a union) until we change
the user visible API (we need to require that A: Copy.

As a temporary solution for arrayvec version 0.4.*, we use zeroed to
initialize an array of bytes, instead of using uninitialized. This may
have a negative performance impact, but the fix is to upgrade to future
arrayvec 0.5.

Author: bluss

src/array_string.rs

@@ -26,6 +26,7 @@ use serde::{Serialize, Deserialize, Serializer, Deserializer};
 /// if needed.
 #[derive(Copy)]
 pub struct ArrayString<A: Array<Item=u8>> {
+    // FIXME: Use Copyable union for xs when we can
     xs: A,
     len: A::Index,
 }
@@ -53,7 +54,8 @@ impl<A: Array<Item=u8>> ArrayString<A> {
     pub fn new() -> ArrayString<A> {
         unsafe {
             ArrayString {
-                xs: ::new_array(),
+                // FIXME: Use Copyable union for xs when we can
+                xs: mem::zeroed(),
                 len: Index::from(0),
             }
         }

src/lib.rs

@@ -74,14 +74,6 @@ pub use array_string::ArrayString;
 pub use errors::CapacityError;
 
 
-unsafe fn new_array<A: Array>() -> A {
-    // Note: Returning an uninitialized value here only works
-    // if we can be sure the data is never used. The nullable pointer
-    // inside enum optimization conflicts with this this for example,
-    // so we need to be extra careful. See `NoDrop` enum.
-    mem::uninitialized()
-}
-
 /// A vector with a fixed capacity.
 ///
 /// The `ArrayVec` is a vector backed by a fixed size array. It keeps track of