1 files changed, 32 insertions, 22 deletions

diff --git a/ecs/src/lock.rs b/ecs/src/lock.rs
index 0b36922..d21b697 100644
--- a/ecs/src/lock.rs
+++ b/ecs/src/lock.rs
@@ -81,21 +81,26 @@ pub struct ReadGuard<'guard, Value>
 
 impl<'guard, Value> ReadGuard<'guard, Value>
 {
-    pub fn map<NewValue>(
-        self,
-        func: impl FnOnce(&Value) -> &NewValue,
-    ) -> MappedReadGuard<'guard, NewValue>
+    pub fn try_map<NewValue>(
+        this: Self,
+        func: impl FnOnce(&Value) -> Option<&NewValue>,
+    ) -> Result<MappedReadGuard<'guard, NewValue>, Self>
     {
-        let value_type_name = self.value_type_name;
+        let value_type_name = this.value_type_name;
 
         // The 'inner' field cannot be moved out of ReadGuard in a normal way since
         // ReadGuard implements Drop
-        let inner = unsafe { std::ptr::read(&self.inner) };
-        forget(self);
-
-        MappedReadGuard {
-            inner: RwLockReadGuard::map(inner, func),
-            value_type_name,
+        let inner = unsafe { std::ptr::read(&this.inner) };
+        forget(this);
+
+        match RwLockReadGuard::try_map(inner, func) {
+            Ok(mapped_guard) => {
+                Ok(MappedReadGuard { inner: mapped_guard, value_type_name })
+            }
+            Err(unmapped_guard) => Err(Self {
+                inner: unmapped_guard,
+                value_type_name,
+            }),
         }
     }
 }
@@ -155,21 +160,26 @@ pub struct WriteGuard<'guard, Value>
 
 impl<'guard, Value> WriteGuard<'guard, Value>
 {
-    pub fn map<NewValue>(
-        self,
-        func: impl FnOnce(&mut Value) -> &mut NewValue,
-    ) -> MappedWriteGuard<'guard, NewValue>
+    pub fn try_map<NewValue>(
+        this: Self,
+        func: impl FnOnce(&mut Value) -> Option<&mut NewValue>,
+    ) -> Result<MappedWriteGuard<'guard, NewValue>, Self>
     {
-        let value_type_name = self.value_type_name;
+        let value_type_name = this.value_type_name;
 
         // The 'inner' field cannot be moved out of ReadGuard in a normal way since
         // ReadGuard implements Drop
-        let inner = unsafe { std::ptr::read(&self.inner) };
-        forget(self);
-
-        MappedWriteGuard {
-            inner: RwLockWriteGuard::map(inner, func),
-            value_type_name,
+        let inner = unsafe { std::ptr::read(&this.inner) };
+        forget(this);
+
+        match RwLockWriteGuard::try_map(inner, func) {
+            Ok(mapped_guard) => {
+                Ok(MappedWriteGuard { inner: mapped_guard, value_type_name })
+            }
+            Err(unmapped_guard) => Err(Self {
+                inner: unmapped_guard,
+                value_type_name,
+            }),
         }
     }
 }