Added class inheritance and constructors. (0.16.0)

examples/class_constructor.fun

@@ -0,0 +1,45 @@
+#!/usr/bin/env fun
+
+/*
+ * This file is part of the Fun programming language.
+ * https://hanez.org/project/fun/
+ *
+ * Copyright 2025 Johannes Findeisen <you@hanez.org>
+ * Licensed under the terms of the Apache-2.0 license.
+ * https://opensource.org/license/apache-2-0
+ *
+ * Added: 2025-10-01
+ */
+
+/*
+ * Demonstrates class constructors named _construct(this, ...)
+ * The constructor is called automatically after instance creation,
+ * receiving 'this' and all header parameters as arguments.
+ */
+
+print("=== class constructor demo ===")
+
+class Counter(number start)
+  // default field value (will be overwritten by _construct)
+  value = 0
+
+  // Runs automatically with (this, start)
+  fun _construct(this, s)
+    this.value = s
+
+  fun inc(this)
+    this.value = this.value + 1
+    return this.value
+
+c = Counter(10)
+print("initial value=" + to_string(c.value))  // expect 10
+print("after inc=" + to_string(c.inc()))      // expect 11
+
+print("=== done ===")
+
+/* Expected output:
+=== class constructor demo === 
+initial value=10
+after inc=11
+=== done ===
+*/