added structs example

Author: BartMassey

README.md

@@ -6,3 +6,4 @@ of these were on the playground, but I prefer to have them
 in a controlled repository now.
 
 * `datatypes`: examples of various datatype thingies
+* `structs.rs`: struct and enum examples

structs.rs

@@ -0,0 +1,60 @@
+/// Examples of structs and enums.
+/// Bart Massey 2021
+
+// Struct example.
+
+#[derive(Debug)]
+struct Point {
+    x: u64,
+    y: u64,
+}
+
+impl Point {                                                          
+    fn x_coord(&self) -> u64 {
+        self.x
+    }
+}
+
+// Tuple struct example.
+
+struct TPoint(u64, u64);
+
+impl TPoint {                                                          
+    fn x_coord(&self) -> u64 {
+        // or "self.0"
+        let TPoint(x, _) = *self;
+        x
+    }
+}                                                                     
+
+// Enum example.
+
+pub enum Color {
+    Red,
+    Green,
+    Blue,
+    Custom(f64, f64, f64),
+}
+
+impl Color {
+    fn red(&self) -> f64 {
+        match self {
+            Color::Red => 1.0,
+            Color::Green => 0.0,
+            Color::Blue => 0.0,
+            Color::Custom(r, _, _) => *r,
+        }
+    }
+}
+
+fn main() {
+    let p = Point { x: 0, y: 0 };
+    println!("{:?}", p);
+    println!("{}", p.x_coord());
+
+    let p = TPoint(0, 0);
+    println!("{}", p.x_coord());
+
+    let c = Color::Custom(0.5, 0.5, 0.0);
+    println!("{}", c.red());
+}