refactor out typemap

core/src/util/mod.rs

@@ -1,19 +1,21 @@
+mod typemap;
 mod arena;
 mod borrow;
 mod change;
-mod slot;
 mod id;
 mod math;
 mod refcount;
+mod slot;
 mod vec2;
 
+pub use typemap::*;
 pub use arena::*;
 pub use borrow::*;
 pub use change::*;
-pub use slot::*;
 pub use id::*;
 pub use math::*;
 pub use refcount::*;
+pub use slot::*;
 pub use vec2::*;
 
 pub type HashMap<K, V> = fxhash::FxHashMap<K, V>;

core/src/util/typemap.rs

@@ -0,0 +1,56 @@
+use crate::util::HashMap;
+use std::{
+    any::TypeId,
+    marker::Unsize,
+    ops::{Deref, DerefMut},
+};
+
+pub struct TypeMap<Trait: ?Sized> {
+    map: HashMap<TypeId, Box<Trait>>,
+}
+
+impl<Trait: ?Sized> TypeMap<Trait> {
+    pub fn set_type<T: Unsize<Trait> + 'static>(&mut self, val: T) {
+        self.map
+            .insert(TypeId::of::<T>(), Box::new(val) as Box<Trait>);
+    }
+
+    pub fn type_mut<T: Unsize<Trait> + 'static>(&mut self) -> Option<&mut T> {
+        Some(Self::convert_mut(self.map.get_mut(&TypeId::of::<T>())?))
+    }
+
+    pub fn type_or_default<T: Default + Unsize<Trait> + 'static>(&mut self) -> &mut T {
+        Self::convert_mut(
+            self.map
+                .entry(TypeId::of::<T>())
+                .or_insert(Box::new(T::default()) as Box<Trait>),
+        )
+    }
+
+    fn convert_mut<T: Unsize<Trait>>(entry: &mut Box<Trait>) -> &mut T {
+        // allegedly this is just what Any does...
+        unsafe { &mut *(entry.as_mut() as *mut Trait as *mut T) }
+    }
+}
+
+impl<T: ?Sized> Deref for TypeMap<T> {
+    type Target = HashMap<TypeId, Box<T>>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.map
+    }
+}
+
+impl<T: ?Sized> DerefMut for TypeMap<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.map
+    }
+}
+
+impl<T: ?Sized> Default for TypeMap<T> {
+    fn default() -> Self {
+        Self {
+            map: Default::default(),
+        }
+    }
+}