type expressions

type_expressions/main.pony

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+actor Main
+    new create(env: Env) =>
+        env.out.print("hlo wld")
+
+// A tuple type is a sequence of types
+var x: (String, U64)
+x = ("hi", 3)
+x = ("bye", 7)
+
+// Pony supports tuple unpacking but calls it "destructuring"
+(var y, var z) = x
+
+// You can access the elements of tuples directly using this
+// one weird syntax
+y = x._1
+z = x._2
+
+// You can't assign elements of tuples. To change the value
+// of a tuple you must reassign the whole thing.
+x = ("wibble wobble", x._2)
+
+// A union is a set of possible types
+// This means "a is a String or None":
+var a: (String | None)
+a = "yeah yeah whatever static analysis tool"
+
+// An intersection is a value that is more than one type at once
+// An example from the standard library:
+// type Map[K: (Hashable box & Comparable[K] box), V] is HashMap[K, V, HashEq[K]]
+// K is Hashable *and* Comparable[K] at the same time