1 files changed, 26 insertions, 0 deletions
diff --git a/engine/src/util.rs b/engine/src/util.rs
index 0c81c71..f18a9c7 100644
--- a/engine/src/util.rs
+++ b/engine/src/util.rs
@@ -68,6 +68,32 @@ impl<Key: Ord, Value> Default for MapVec<Key, Value>
     }
 }
 
+pub trait OptionExt<T>
+{
+    /// Substitute for the currently experimental function
+    /// [`Option::get_or_try_insert_with`].
+    /// See https://github.com/rust-lang/rust/issues/143648
+    fn get_or_try_insert_with_fn<Err>(
+        &mut self,
+        func: impl Fn() -> Result<T, Err>,
+    ) -> Result<&mut T, Err>;
+}
+
+impl<T> OptionExt<T> for Option<T>
+{
+    fn get_or_try_insert_with_fn<Err>(
+        &mut self,
+        func: impl FnOnce() -> Result<T, Err>,
+    ) -> Result<&mut T, Err>
+    {
+        if let None = self {
+            *self = Some(func()?);
+        }
+
+        Ok(unsafe { self.as_mut().unwrap_unchecked() })
+    }
+}
+
 macro_rules! try_option {
     ($expr: expr) => {
         match $expr {