diff --git a/core/src/lib.rs b/core/src/lib.rs
index f3cf313..b512ae9 100644
--- a/core/src/lib.rs
+++ b/core/src/lib.rs
@@ -16,6 +16,29 @@ pub type Perhaps<T> = Result<Option<T>, Box<dyn Error>>;
 }
 
 pub trait Has<T>: Send + Sync {
-    fn get     (&self) -> &T;
+    fn get     (&self)     -> &T;
     fn get_mut (&mut self) -> &mut T;
 }
+
+#[macro_export] macro_rules! has {
+    ($T:ty: |$self:ident : $S:ty| $x:expr) => {
+        impl Has<$T> for $S {
+            fn get     (&$self)     -> &$T     { &$x }
+            fn get_mut (&mut $self) -> &mut $T { &mut $x }
+        }
+    };
+}
+
+pub trait MaybeHas<T>: Send + Sync {
+    fn get     (&self)     -> Option<&T>;
+    fn get_mut (&mut self) -> Option<&mut T>;
+}
+
+#[macro_export] macro_rules! maybe_has {
+    ($T:ty: |$self:ident : $S:ty| $x:block; $y:block $(;)?) => {
+        impl MaybeHas<$T> for $S {
+            fn get     (&$self)     -> Option<&$T>     $x
+            fn get_mut (&mut $self) -> Option<&mut $T> $y
+        }
+    };
+}