class Man : public Base {
public:
	int getSpeakRes(SpeakBase& speak) {
		return speak.speakWord(this);  //编译器知道this是哪个类型实例
	}
}

class Ghost : public Base {
public:
	int getSpeakRes(SpeakBase& speak) {
		return speak.speakWord(this);
	}
}

class Speak : public SpeakBase {
public:
	int speakWord(Man& man) {
		return "Man"; 
	}
	int speakWord(Ghost& ghost) {
		return "Ghost"; 
	}
}

class Board {
    drawFigure(aFigure) {
        aFigure.getDrawnOn(this)
    }
    drawTriangle(aTriangle) {
        // ...
    }
    drawSquare(aSquare) {
        // ...
    }
}

class Triangle extends Figure {
    getDrawnOn(aDrawableSurface) {
        aDrawableSurface.drawTriangle(this)
    }
}

class Square extends Figure {
    getDrawnOn(aDrawableSurface) {
        aDrawableSurface.drawSquare(this)
    }
}


----

let board = new Board();
let triangle = new Triangle();

board.drawFigure(triangle)