Add compatibilty with rust-stable.

  * Add feature flag for const-fn functionality, which simplifies some
    things and lets this crate run on architectures where atomic CAS
    isn't available (e.g., thumbv6).

  * Remove `const fn` where necessary to compile under rust-stable.

  * BREAKING CHANGE - Change signature of `Handler::replace` to take a
    mutable borrow. This is required because the underlying type is
    now a NonNull, which needs `mut`. The old behavior was never
    desired, but a consequence of trying to avoid `Option` by using a
    default handler.

  * Use lazy_static crate for initialization of Handler/HandlerArray.

  * Specify Sync for Handler. This is not amazing, since it isn't, but
    it's necessary for initialization in static contexts inside
    `lazy_static`. This should be fine, because any actual
    manipulation of the handler is done in unsafe functions.

2 files changed, 14 insertions, 4 deletions

diff --git a/examples/dummy.rs b/examples/dummy.rs
index 7e7c237..cfcd717 100644
--- a/examples/dummy.rs
+++ b/examples/dummy.rs
@@ -1,24 +1,29 @@
 use clint::Handler;
 
+#[macro_use]
+extern crate lazy_static;
+
 // Wrapper used to call through to `example_handler` via `closure` in
 // `main`. `Handler::new()` places a do-nothing handler in this at
 // compile-time, in case the interrupt using this handler is fired
 // before being `replace`d in `main`.
-static mut HANDLER: Handler = Handler::new();
+lazy_static! {
+    static ref HANDLER: Handler<'static> = Handler::new();
+}
 
 fn main() {
     let mut x: u32 = 0;
 
     // Create a closure to take a mutable reference to `x` for use in
     // `example_handler`.
-    let closure = move || example_handler(&mut x);
+    let mut closure = move || example_handler(&mut x);
 
     // Swap out the do-nothing handler with our closure that calls
     // through to `example_handler`. Ideally, the interrupt which uses
     // this handler would be disabled while this happens, but as this
     // is a demo, and there aren't any actual interrupts firing, this
     // is left as an exercise to the reader.
-    unsafe { HANDLER.replace(&closure) };
+    unsafe { HANDLER.replace(&mut closure) };
 
     // Simulate firing the interrupt.
     dummy_interrupt();
diff --git a/examples/scope.rs b/examples/scope.rs
index cd17570..8df0702 100644
--- a/examples/scope.rs
+++ b/examples/scope.rs
@@ -1,6 +1,11 @@
 use clint::HandlerArray;
 
-static HANDLERS: HandlerArray = HandlerArray::new();
+#[macro_use]
+extern crate lazy_static;
+
+lazy_static! {
+    static ref HANDLERS: HandlerArray<'static> = HandlerArray::new();
+}
 
 fn main() {
     let mut cl = || println!("whoa!");