void-payloads, multi-pattern arms, and range patterns (match statements)

examples/programs/match/main.bro

@@ -4,7 +4,8 @@ Animal :: enum {
 	bird
 }
 
-# tagged union over an existing enum (variants are a subset of the enum's members)
+# tagged union over an existing enum (variants are a subset of the enum's members);
+# dog and bird share the same payload type (i32), so a multi-pattern arm may capture both.
 Data :: union(Animal) {
 	dog  i32
 	bird i32
@@ -16,6 +17,17 @@ Shape :: union(enum) {
 	circle i32 # radius
 }
 
+Point :: struct {
+	x i32
+	y i32
+}
+
+# tagged union with a void-payload variant (`empty` carries no value)
+Box :: union(enum) {
+	point Point
+	empty void
+}
+
 # Statement match with payload capture; every variant returns, so the function needs
 # no trailing return (the desugared if/else chain covers all paths).
 describe :: func(d Data) i32 {
@@ -37,39 +49,67 @@ area :: func(s Shape) i32 {
 	return result
 }
 
+# Same-type multi-pattern capture: `.dog` and `.bird` are both i32, so one capture binds
+# either payload (read once at the union's shared carrier offset).
+payload_of :: func(d Data) i32 {
+	v :: match d {
+		.dog, .bird |n|: n
+	}
+	return v
+}
+
 main :: func() i32 {
+	acc i32 = 0
+
 	dog Data = Data{ dog = 9 }
 	bird Data = Data{ bird = 38 }
-	total i32 = describe(dog) + describe(bird) # 10 + 40 = 50
+	acc = acc + describe(dog) + describe(bird) # 10 + 40 = 50
 
-	# enum statement match, exhaustive without an `else`
+	# same-type multi-pattern capture
+	acc = acc + payload_of(dog) + payload_of(bird) # 9 + 38 = 47
+
+	# enum statement match, exhaustive, with a multi-pattern arm
 	a Animal = .bird
 	rank i32 = 0
 	match a {
-		.dog: rank = 1
-		.cat: rank = 2
-		.bird: rank = 3
+		.dog, .cat: rank = 1
+		.bird:      rank = 3
 	}
+	acc = acc + rank # +3
 
-	# enum value match
+	# enum value match with a multi-pattern arm
 	legs :: match a {
-		.dog: 4
-		.cat: 4
-		.bird: 2
+		.dog, .cat: 4
+		.bird:      2
 	}
+	acc = acc + legs # +2
 
-	# integer match with a mandatory `else`
+	# scalar match: a range arm, a multi-literal arm, and a mandatory else
 	bucket i32 = 0
 	match rank {
-		1: bucket = 100
-		3: bucket = 5
-		else: bucket = 99
+		0..3:  bucket = 1  # exclusive 0,1,2 — does not include 3
+		3, 4:  bucket = 5  # rank is 3
+		else:  bucket = 99
 	}
+	acc = acc + bucket # +5
 
-	sq Shape = Shape{ square = 4 }
-	ci Shape = Shape{ circle = 2 }
-	shapes i32 = area(sq) + area(ci) # 16 + 12 = 28
+	# void-payload variant: bare-key construction + a no-capture arm
+	e Box = Box{ empty }
+	hit i32 = 0
+	match e {
+		.point |pt|: hit = pt.x
+		.empty:      hit = 7
+	}
+	acc = acc + hit # +7
 
-	# 50 + 3 + 2 + 5 + 28 = 88
-	return total + rank + legs + bucket + shapes - 88
+	# pointer capture mutates the subject's payload in place
+	b Box = Box{ point = Point{ x = 1, y = 2 } }
+	match b {
+		.point |@p|: p.x = 10
+		.empty:      hit = hit
+	}
+	acc = acc + b.point.x # +10 (mutated through the @mut Point)
+
+	# 50 + 47 + 3 + 2 + 5 + 7 + 10 = 124
+	return acc - 124
 }