Merge pull request #40 from lufterc/property-export-options

Add info about property attribute options

Author: Bromeon

src/rust-binding/properties.md

@@ -18,3 +18,71 @@ print("enemies: ", api.enemy_count)
 ```
 
 That's it.
+
+## Export options
+
+The `#[property]` attribute can accept a several options to refine the export behavior.
+
+You can specify default property value with the following argument:
+
+```rust
+#[property(default = 10)]
+enemy_count: i32,
+```
+
+If you need to hide this property in Godot editor, use `no_editor` option:
+
+```rust
+#[property(no_editor)]
+enemy_count: i32,
+```
+
+## Property access hooks
+
+You can add hooks to call methods before and after property value was retrieved or changed.
+
+Note that unlike [GDScript's `setget` keyword](https://docs.godotengine.org/en/3.3/getting_started/scripting/gdscript/gdscript_basics.html?#setters-getters), this does _not_ register a custom setter or getter. Instead, it registers a callback which is invoked _before or after_ the set/get occurs, and lacks both parameter and return value.
+
+```rust
+#[derive(NativeClass, Default)]
+#[inherit(Node)]
+struct GodotApi {
+    // before get
+    #[property(before_get = "Self::before_get")]
+    prop_before_get: i32,
+
+    // before set
+    #[property(before_set = "Self::before_set")]
+    prop_before_set: i32,
+
+    // after get
+    #[property(after_get = "Self::after_get")]
+    prop_after_get: i32,
+
+    // after set
+    #[property(after_set = "Self::after_set")]
+    prop_after_set: i32,
+}
+
+impl GodotApi {
+    fn new(_owner: &Node) -> Self {
+        Self::default()
+    }
+
+    fn before_get(&self, _owner: TRef<Node>) {
+        godot_print!("Before get");
+    }
+
+    fn before_set(&self, _owner: TRef<Node>) {
+        godot_print!("Before set");
+    }
+
+    fn after_get(&self, _owner: TRef<Node>) {
+        godot_print!("After get");
+    }
+
+    fn after_set(&self, _owner: TRef<Node>) {
+        godot_print!("After set");
+    }
+}
+```