Add a ref_slice module.

Utility functions for converting &T to an &[T] slice with a single
element.

lib/cretonne/src/lib.rs

@@ -21,3 +21,4 @@ mod write;
 mod constant_hash;
 mod predicates;
 mod legalizer;
+mod ref_slice;

lib/cretonne/src/ref_slice.rs

@@ -0,0 +1,18 @@
+//! Functions for converting a reference into a singleton slice.
+//!
+//! See also the ref_slice crate on crates.io.
+//!
+//! We define the functions here to avoid external dependencies, and to ensure that they are
+//! inlined in this crate.
+//!
+//! Despite their using an unsafe block, these functions are completely safe.
+
+use std::slice;
+
+pub fn ref_slice<T>(s: &T) -> &[T] {
+    unsafe { slice::from_raw_parts(s, 1) }
+}
+
+pub fn ref_slice_mut<T>(s: &mut T) -> &mut [T] {
+    unsafe { slice::from_raw_parts_mut(s, 1) }
+}