1 files changed, 68 insertions, 0 deletions
diff --git a/src/components/macros/macros.rs b/src/components/macros/macros.rs
index 9203567075b..76ceb8d1515 100644
--- a/src/components/macros/macros.rs
+++ b/src/components/macros/macros.rs
@@ -9,6 +9,11 @@
 
 #![feature(macro_rules)]
 
+
+#[cfg(test)]
+extern crate sync;
+
+
 #[macro_export]
 macro_rules! bitfield(
     ($bitfieldname:ident, $getter:ident, $setter:ident, $value:expr) => (
@@ -28,3 +33,66 @@ macro_rules! bitfield(
     )
 )
 
+
+#[macro_export]
+macro_rules! lazy_init(
+    ($(static ref $N:ident : $T:ty = $e:expr;)*) => (
+        $(
+            #[allow(non_camel_case_types)]
+            struct $N {__unit__: ()}
+            static $N: $N = $N {__unit__: ()};
+            impl Deref<$T> for $N {
+                fn deref<'a>(&'a self) -> &'a $T {
+                    unsafe {
+                        static mut s: *$T = 0 as *$T;
+                        static mut ONCE: ::sync::one::Once = ::sync::one::ONCE_INIT;
+                        ONCE.doit(|| {
+                            s = ::std::cast::transmute::<~$T, *$T>(~($e));
+                        });
+                        &*s
+                    }
+                }
+            }
+
+        )*
+    )
+)
+
+
+#[cfg(test)]
+mod tests {
+    extern crate collections;
+
+    lazy_init! {
+        static ref NUMBER: uint = times_two(3);
+        static ref VEC: [~uint, ..3] = [~1, ~2, ~3];
+        static ref OWNED_STRING: ~str = ~"hello";
+        static ref HASHMAP: collections::HashMap<uint, &'static str> = {
+            let mut m = collections::HashMap::new();
+            m.insert(0u, "abc");
+            m.insert(1, "def");
+            m.insert(2, "ghi");
+            m
+        };
+    }
+
+    fn times_two(n: uint) -> uint {
+        n * 2
+    }
+
+    #[test]
+    fn test_basic() {
+        assert_eq!(*OWNED_STRING, ~"hello");
+        assert_eq!(*NUMBER, 6);
+        assert!(HASHMAP.find(&1).is_some());
+        assert!(HASHMAP.find(&3).is_none());
+        assert_eq!(VEC.as_slice(), &[~1, ~2, ~3]);
+    }
+
+    #[test]
+    fn test_repeat() {
+        assert_eq!(*NUMBER, 6);
+        assert_eq!(*NUMBER, 6);
+        assert_eq!(*NUMBER, 6);
+    }
+}