feat: mention struct update syntax

src/language/custom-types/members.md

@@ -309,10 +309,11 @@ Console.WriteLine(pt.ToString()); // prints: Point { X = 789, Y = 456 }
 readonly record struct Point(int X, int Y);
 ```
 
-There is no `with` in Rust, but to emulate something similar in Rust, it has
-to be baked into the type's design:
+There is no `with` in Rust, but the struct update syntax can be used
+similar. This moves the original value, however:
 
 ```rust
+#[derive(Debug)]
 struct Point { x: i32, y: i32 }
 
 impl Point {
@@ -322,10 +323,11 @@ impl Point {
 
     pub fn x(&self) -> i32 { self.x }
     pub fn y(&self) -> i32 { self.y }
+}
 
-    // following methods consume self and return a new instance
-
-    pub fn set_x(self, val: i32) -> Self { Self::new(val, self.y) }
-    pub fn set_y(self, val: i32) -> Self { Self::new(self.x, val) }
+fn main() {
+    let pt = Point::new(123, 456);
+    let pt = Point { x: 789, ..pt };
+    println!("{pt:?}"); // prints: Point { x: 789, y: 456 }
 }
 ```