On 5/1/07, pedr browne <[EMAIL PROTECTED]> wrote:
Hi,
A have a Factory that needs to instanciate Objects with differing numbers of
parameters (1-4). Is there any way to deal with this situation and maintain
strong typing.
private function createItem(param_ob:Object, key:String):Void{
switch(key){
case "item_1":
myItem = new Item_1(param_ob.width, param_ob.y);
break
case "item2":
myItem = new Item_2(param_ob.height, param_ob.color);
break
etc...
}
}
(Why is the factory method private?)
One way is to split it into two functions:
public function static createFromWidthY(width:Number, y:Number):Item {
return new Item1(width, y);
}
public function static createFromHeightColor(height:Number, color:Number):Item {
return new Item2(height, color);
}
(Or call them createItem1 and createItem2 or whatever.)
Another way is to use classes for parameter types:
// Make an "abstract" class for parameters:
class myPackage.ItemParams extends Object {
private function ItemParams() {
super();
}
}
// Then make "concrete" subclasses for specific types of parameters:
class myPackage.WidthYParams extends ItemParams {
public function WidthYParams(width:Number, y:Number) {
super();
this.width = width;
this.y = y;
}
public function get width():Number {
return _width;
}
public function set width(value:Number):Void {
if (isFinite(value)) {
_width = value;
}
}
public function get y():Number {
return _y;
}
public function set y(value:Number):Void {
if (isFinite(value)) {
_y = value;
}
}
private var _width:Number = 0;
private var _y:Number = 0;
}
class myPackage.HeightColorParams extends ItemParams {
public function HeightColorParams (height:Number, color:Number) {
super();
this.height= height;
this.color = color;
}
public function get color():Number {
return _color;
}
public function set color(value:Number):Void {
if (isFinite(value)) {
_color = Math.min(0xFFFFFF, Math.max(0, Math.floor(value)));
}
}
public function get height():Number {
return _height;
}
public function set height(value:Number):Void {
if (isFinite(value)) {
_height = value;
}
}
private var _color:Number = 0;
private var _height:Number = 0;
}
// Then, in your factory method:
public static function createItem(params:ItemParams):Item {
if (!(params instanceof ItemParams)) {
throw new Error("Invalid argument in call to
MyFactory.createItem: " + params);
}
if (params instanceof WidthYParams) {
return new Item1(WidthYParams(params).width, WidthYParams(params).y);
}
if (params instanceof HeightColorParams) {
return new Item2(HeightColorParams(params).height,
HeightColorParams(params).color);
}
throw new Error("Unrecognized item parameters: " + params);
}
--
T. Michael Keesey
Director of Technology
Exopolis, Inc.
2894 Rowena Avenue Ste. B
Los Angeles, California 90039
--
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