Mercurial > repos > alg_tools / file diff

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/metaprogramming.rs	Mon Feb 03 19:22:16 2025 -0500
@@ -0,0 +1,41 @@
+/*!
+Metaprogramming tools
+*/
+
+/// Reference `x` if so indicated by the first parameter.
+/// Typically to be used from another macro.
+///
+/// ```ignore
+/// maybe_ref!(ref, V)   // ➡ &V
+/// maybe_ref!(noref, V) // ➡ V
+/// ```
+#[macro_export]
+macro_rules! maybe_ref {
+    (ref, $x:expr) => { &$x };
+    (noref, $x:expr) => { $x };
+    (ref, $x:ty) => { &$x };
+    (noref, $x:ty) => { $x };
+}
+
+/// Choose `a` if first argument is the literal `ref`, otherwise `b`.
+#[macro_export]
+macro_rules! ifref {
+    (noref, $a:expr, $b:expr) => { $b };
+    (ref, $a:expr, $b:expr) => { $a };
+}
+
+
+/// Annotate `x` with a lifetime if the first parameter
+/// Typically to be used from another macro.
+///
+/// ```ignore
+/// maybe_ref!(ref, &'a V)    // ➡ &'a V
+/// maybe_ref!(noref, &'a V)  // ➡ V
+/// ```
+#[macro_export]
+macro_rules! maybe_lifetime {
+    (ref, $x:ty) => { $x };
+    (noref, &$lt:lifetime $x:ty) => { $x };
+    (noref, &$x:ty) => { $x };
+}
+