doc: mention struct-like enum variants /cc #4217

Author: catamorphism

doc/rust.md

@@ -1107,6 +1107,19 @@ let mut a: Animal = Dog;
 a = Cat;
 ~~~~
 
+Enumeration constructors can have either named or unnamed fields:
+~~~~
+enum Animal {
+    Dog (~str, float),
+    Cat { name: ~str, weight: float }
+}
+
+let mut a: Animal = Dog(~"Cocoa", 37.2);
+a = Cat{ name: ~"Spotty", weight: 2.7 };
+~~~~
+
+In this example, `Cat` is a _struct-like enum variant_,
+whereas `Dog` is simply called an enum variant.
 ### Constants
 
 ~~~~~~~~ {.ebnf .gram}

doc/tutorial.md

@@ -733,6 +733,24 @@ fn point_from_direction(dir: Direction) -> Point {
 }
 ~~~~
 
+A special kind of enum variant, called _struct-like enums_,
+can have its fields extracted with dot notation and not just destructuring.
+For example:
+
+~~~~
+# struct Point {x: float, y: float}
+# fn square(x: float) -> float { x * x }
+enum Shape {
+    Circle { center: Point, radius: float },
+    Rectangle { left: Point, right: Point }
+}
+fn area(sh: Shape) -> float {
+   match sh {
+      Circle(c) => float::consts::pi * square(c.radius),
+      Rectangle(r) => r.right.x - r.left.x * r.right.y - r.right.y
+   }
+}
+~~~~
 ## Tuples
 
 Tuples in Rust behave exactly like structs, except that their fields