coffeeScript中类的多态［学习篇］

class Shape
constructor: (@width) ->
computeArea: -> throw new Error 'I am an abstract class!'

class Square extends Shape
computeArea: -> Math.pow @width, 2

class Circle extends Shape
radius: -> @width / 2
computeArea: -> Math.PI * Math.pow @radius, 2

showArea = (shape) ->
unless shape instanceof Shape
throw new Error 'showArea requires a Shape instance!'
console.log shape.computeArea()

showArea new Square(2) #4
showArea new Circle(2) #pi

// Generated by CoffeeScript 1.10.0
var Circle, Shape, Square, showArea,
extend = function(child, parent) { for (var key in parent) { if (hasProp.call(parent, key)) child[key] = parent[key]; } function ctor() { this.constructor = child; } ctor.prototype = parent.prototype; child.prototype = new ctor(); child.__super__ = parent.prototype; return child; },
hasProp = {}.hasOwnProperty;

Shape = (function() {
function Shape(width) {
this.width = width;
}

Shape.prototype.computeArea = function() {
throw new Error('I am an abstract class!');
};

return Shape;

})();

Square = (function(superClass) {
extend(Square, superClass);

function Square() {
return Square.__super__.constructor.apply(this, arguments);
}

Square.prototype.computeArea = function() {
return Math.pow(this.width, 2);
};

return Square;

})(Shape);

Circle = (function(superClass) {
extend(Circle, superClass);

function Circle() {
return Circle.__super__.constructor.apply(this, arguments);
}

Circle.prototype.radius = function() {
return this.width / 2;
};

Circle.prototype.computeArea = function() {
return Math.PI * Math.pow(this.radius, 2);
};

return Circle;

})(Shape);

showArea = function(shape) {
if (!(shape instanceof Shape)) {
throw new Error('showArea requires a Shape instance!');
}
return console.log(shape.computeArea());
};

showArea(new Square(2));

showArea(new Circle(2));