Add harp::once!

Author: lionel-

crates/harp/src/lib.rs

@@ -73,9 +73,9 @@ pub(crate) use harp::fixtures::r_task;
 pub use harp::object::list_get;
 pub use harp::object::list_poke;
 pub use harp::object::RObject;
+pub use harp::options::*;
 pub use harp::session::*;
 pub use harp::symbol::RSymbol;
-pub use harp::options::*;
 pub use harp::weak_ref::RWeakRef;
 pub use harp_macros::register;
 
@@ -258,6 +258,28 @@ macro_rules! push_rds {
     };
 }
 
+/// Allocate global variable for the R thread with lazy init
+///
+/// Uses thread_local storage to avoid issues with SEXP being non-Sync.
+/// Usage:
+///
+/// ```
+/// harp::once! {
+///     static NAME: Type = initialization_expression;
+/// }
+/// NAME.with(|x| foo(x));
+/// ```
+///
+/// Expands to a thread-local static initialized on first access in the thread.
+#[macro_export]
+macro_rules! once {
+    ( $( static $name:ident : $ty:ty = $init:expr );* $(;)? ) => {
+        thread_local! {
+            $( static $name: $ty = $init; )*
+        }
+    };
+}
+
 #[cfg(test)]
 mod tests {
     use libr::*;

crates/harp/src/parser/srcref.rs

@@ -139,7 +139,7 @@ impl SrcFile {
 
         let inner: RObject = inner.into();
 
-        thread_local! {
+        harp::once! {
             static CLASS: RObject = crate::CharacterVector::create(vec!["srcfile", "srcfilecopy"]).into();
         }
         CLASS.with(|c| inner.set_attribute("class", c.sexp));