print("\n--- Test: Practical Polymorphism ---");

// Example 1: Shapes - compute total area
class Shape { func area() { return 0; } }
class Rectangle extends Shape { func init(w, h) { this.w = w; this.h = h; } func area() { return this.w * this.h; } }
class Triangle extends Shape { func init(b, h) { this.b = b; this.h = h; } func area() { return (this.b * this.h) / 2; } }

var shapes = [ Rectangle(3, 4), Triangle(10, 2), Rectangle(5, 2) ];
var total = 0;
for (var i = 0; i < shapes.len(); i = i + 1) { total = total + shapes[i].area(); }
assert(total == (3*4) + (10*2)/2 + (5*2), "shapes total area");

// Example 2: Logger hierarchy - override behavior
class Logger { func log(msg) { return "[LOG] " + msg; } }
class ConsoleLogger extends Logger { func log(msg) { return "[CONSOLE] " + msg; } }
class FileLogger extends Logger { func log(msg) { return "[FILE] " + msg; } }
var loggers = [ Logger(), ConsoleLogger(), FileLogger() ];
assert(loggers[0].log("ok") == "[LOG] ok", "base logger");
assert(loggers[1].log("ok") == "[CONSOLE] ok", "console logger");
assert(loggers[2].log("ok") == "[FILE] ok", "file logger");

// Example 3: Notifier with extension-based specialization
class Notifier { func send(msg) { return "sent:" + msg; } }
class EmailNotifier extends Notifier {}
class SmsNotifier extends Notifier {}
extension EmailNotifier { func send(msg) { return super.send("EMAIL:" + msg); } }
extension SmsNotifier { func send(msg) { return super.send("SMS:" + msg); } }
var n = [ EmailNotifier(), SmsNotifier(), Notifier() ];
assert(n[0].send("hello") == "sent:EMAIL:hello", "email notify");
assert(n[1].send("hello") == "sent:SMS:hello", "sms notify");
assert(n[2].send("hello") == "sent:hello", "base notify");

// Example 4: Processor pipeline - same method name, different implementations
class Processor { func process(x) { return x; } }
class DoubleProc extends Processor { func process(x) { return x * 2; } }
class IncProc extends Processor { func process(x) { return x + 1; } }
var pipeline = [ DoubleProc(), IncProc(), DoubleProc() ]; // (((3*2)+1)*2) = 14
var value = 3;
for (var i = 0; i < pipeline.len(); i = i + 1) { value = pipeline[i].process(value); }
assert(value == 14, "processor pipeline");

print("Practical polymorphism: PASS");