1 files changed, 25 insertions, 0 deletions
diff --git a/incria/src/mapping.rs b/incria/src/mapping.rs
new file mode 100644
index 0000000..6cfac67
--- /dev/null
+++ b/incria/src/mapping.rs
@@ -0,0 +1,25 @@
+use std::ops::Deref;
+
+/// A mapper of keys to values, that memoises the results and re-evaluates when necessary.
+///
+/// This mapping can be:
+///   * Storage or access of externally-modifiable values like files or resources shared with other threads (cells)
+///   * Computations that are pure, except for their use of cells above (thunks)
+///
+/// Mappers should be mainly responsible for tracking and re-performing new computations as appropriate, using the API in [`crate::deps`].
+pub trait Mapper {
+    /// The key or input type
+    type Key;
+
+    /// The result
+    type Value;
+
+    /// A wrapper around the result.
+    /// This allows things like read guards or Arcs to be returned, so long as they dereference to the correct type.
+    type Wrapper<'a>: Deref<Target = Self::Value> + 'a
+    where
+        Self::Value: 'a;
+
+    /// Get a value by the given key, calculating it if necessary.
+    async fn get<'a>(&'a self, key: &Self::Key) -> Self::Wrapper<'a>;
+}