Introduce opaque window::Id type

native/src/window.rs

@@ -1,10 +1,12 @@
 //! Build window-based GUI applications.
 mod action;
 mod event;
+mod id;
 mod mode;
 mod user_attention;
 
 pub use action::Action;
 pub use event::Event;
+pub use id::Id;
 pub use mode::Mode;
 pub use user_attention::UserAttention;

native/src/window/id.rs

@@ -0,0 +1,16 @@
+use std::collections::hash_map::DefaultHasher;
+use std::hash::{Hash, Hasher};
+
+#[derive(Debug, PartialEq, Eq, Hash)]
+/// TODO(derezzedex)
+pub struct Id(u64);
+
+impl Id {
+    /// TODO(derezzedex)
+    pub fn new(id: impl Hash) -> Id {
+        let mut hasher = DefaultHasher::new();
+        id.hash(&mut hasher);
+
+        Id(hasher.finish())
+    }
+}