1 files changed, 120 insertions, 2 deletions
diff --git a/ecs/src/lock.rs b/ecs/src/lock.rs
index 74b0415..c700098 100644
--- a/ecs/src/lock.rs
+++ b/ecs/src/lock.rs
@@ -1,7 +1,13 @@
-use std::mem::transmute;
+use std::mem::{forget, transmute};
 use std::ops::{Deref, DerefMut};
 
-use parking_lot::{RwLock, RwLockReadGuard, RwLockWriteGuard};
+use parking_lot::{
+    MappedRwLockReadGuard,
+    MappedRwLockWriteGuard,
+    RwLock,
+    RwLockReadGuard,
+    RwLockWriteGuard,
+};
 
 use crate::type_name::TypeName;
 
@@ -79,6 +85,23 @@ impl<'guard, Value> ReadGuard<'guard, Value>
 where
     Value: TypeName,
 {
+    pub fn map<NewValue>(
+        self,
+        func: impl FnOnce(&Value) -> &NewValue,
+    ) -> MappedReadGuard<'guard, NewValue>
+    where
+        NewValue: TypeName,
+    {
+        // 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),
+        }
+    }
+
     /// Converts the `ReadGuard` to a `ReadGuard` with a possibly longer lifetime.
     ///
     /// # Safety
@@ -114,6 +137,36 @@ where
 }
 
 #[derive(Debug)]
+pub struct MappedReadGuard<'guard, Value>
+where
+    Value: TypeName,
+{
+    inner: MappedRwLockReadGuard<'guard, Value>,
+}
+
+impl<'guard, Value> Deref for MappedReadGuard<'guard, Value>
+where
+    Value: TypeName,
+{
+    type Target = Value;
+
+    fn deref(&self) -> &Self::Target
+    {
+        &self.inner
+    }
+}
+
+impl<'guard, Value> Drop for MappedReadGuard<'guard, Value>
+where
+    Value: TypeName,
+{
+    fn drop(&mut self)
+    {
+        tracing::trace!("Dropped mapped lock to value of type {}", self.type_name());
+    }
+}
+
+#[derive(Debug)]
 pub struct WriteGuard<'guard, Value>
 where
     Value: TypeName,
@@ -121,6 +174,28 @@ where
     inner: RwLockWriteGuard<'guard, Value>,
 }
 
+impl<'guard, Value> WriteGuard<'guard, Value>
+where
+    Value: TypeName,
+{
+    pub fn map<NewValue>(
+        self,
+        func: impl FnOnce(&mut Value) -> &mut NewValue,
+    ) -> MappedWriteGuard<'guard, NewValue>
+    where
+        NewValue: TypeName,
+    {
+        // 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),
+        }
+    }
+}
+
 impl<'guard, Value> Deref for WriteGuard<'guard, Value>
 where
     Value: TypeName,
@@ -152,3 +227,46 @@ where
         tracing::trace!("Dropped mutable lock to value of type {}", self.type_name());
     }
 }
+
+#[derive(Debug)]
+pub struct MappedWriteGuard<'guard, Value>
+where
+    Value: TypeName,
+{
+    inner: MappedRwLockWriteGuard<'guard, Value>,
+}
+
+impl<'guard, Value> Deref for MappedWriteGuard<'guard, Value>
+where
+    Value: TypeName,
+{
+    type Target = Value;
+
+    fn deref(&self) -> &Self::Target
+    {
+        &self.inner
+    }
+}
+
+impl<'guard, Value> DerefMut for MappedWriteGuard<'guard, Value>
+where
+    Value: TypeName,
+{
+    fn deref_mut(&mut self) -> &mut Self::Target
+    {
+        &mut self.inner
+    }
+}
+
+impl<'guard, Value> Drop for MappedWriteGuard<'guard, Value>
+where
+    Value: TypeName,
+{
+    fn drop(&mut self)
+    {
+        tracing::trace!(
+            "Dropped mapped mutable lock to value of type {}",
+            self.type_name()
+        );
+    }
+}