core: add as_ref

core/src/lib.rs

@@ -1,13 +1,18 @@
 mod core_macros;
 pub(crate) use std::error::Error;
+
 /// Standard result type.
 pub type Usually<T> = Result<T, Box<dyn Error>>;
+
 /// Standard optional result type.
 pub type Perhaps<T> = Result<Option<T>, Box<dyn Error>>;
+
 /// Type-dispatched `get` and `get_mut`.
 pub trait Has<T>: Send + Sync { fn get (&self) -> &T; fn get_mut (&mut self) -> &mut T; }
+
 /// Type-dispatched `get` and `get_mut` that return an [Option]-wrapped result.
 pub trait MaybeHas<T>: Send + Sync { fn get (&self) -> Option<&T>; fn get_mut (&mut self) -> Option<&mut T>; }
+
 /// May compute a `RetVal` from `Args`.
 pub trait Eval<Args, RetVal> {
     /// A custom operation on [Args] that may return [Result::Err] or [Option::None].
@@ -22,3 +27,11 @@ pub trait Eval<Args, RetVal> {
         }
     }
 }
+
+#[macro_export] macro_rules! as_ref {
+    ($T:ty: |$self:ident : $S:ty| $x:expr) => {
+        impl AsRef<$T> for $S {
+            fn as_ref (&$self) -> &$T { &$x }
+        }
+    };
+}