Make Id a proper newtype

emigui/src/id.rs

@@ -0,0 +1,29 @@
+use std::{collections::hash_map::DefaultHasher, hash::Hash};
+
+#[derive(Clone, Copy, Debug, Hash, Eq, PartialEq)]
+pub struct Id(u64);
+
+impl Id {
+    pub fn whole_screen() -> Self {
+        Self(0)
+    }
+
+    pub fn popup() -> Self {
+        Self(1)
+    }
+
+    pub fn new<H: Hash>(source: &H) -> Id {
+        use std::hash::Hasher;
+        let mut hasher = DefaultHasher::new();
+        source.hash(&mut hasher);
+        Id(hasher.finish())
+    }
+
+    pub fn with<H: Hash>(self, child: &H) -> Id {
+        use std::hash::Hasher;
+        let mut hasher = DefaultHasher::new();
+        hasher.write_u64(self.0);
+        child.hash(&mut hasher);
+        Id(hasher.finish())
+    }
+}