ImplementsDynamic.hx

package myApp;

class ImplementsDynamic
	implements Dynamic<String> {
	public var present:Int;
	public function new() {}
}

Main.hx

package myApp;

// import myApp.ImplementsDynamic;

class Main {
	static public function main() {
		var c = new myApp.ImplementsDynamic();
		// valid, present is an existing field
		c.present = 1;
		// valid, assigned value is a String
		c.stringField = "foo";
		// error, Int should be String
		// c.intField = 1;
		trace(c.stringField);
	}
}