I have a question about the magic methods getter and setter.
My question is: What is better (faster, safer)?
P.S. This is ActionScript 3, but the question can be answered for other languages like PHP, JavaScript, C# also.
case 1
public class Test extends Sprite
{
private var _test : uint = 0;
public function Test()
{
start();
}
private function start() : void
{
trace(_test); ** Take the private var _test **
}
public function set test(value : uint) : void
{
_test = value;
start();
}
public function get test() : uint
{
return _test;
}
}
or case 2
public class Test extends Sprite
{
private var _test : uint = 0;
public function Test()
{
start();
}
private function start() : void
{
trace(test); ** difference here, take the public function test **
}
public function set test(value : uint) : void
{
_test = value;
start();
}
public function get test() : uint
{
return _test;
}
}
What is the best (fastest) way?
Thanks!
You're about 90% of the way to writing your own test case to find out yourself..
Getters and setters are intended to add control over what happens when a property is set or retrieved or to create read-only or write-only properties.
These benefits greatly outweigh any possible performance differences.
As for those performance differences, here is a test environment:
// Test property.
var _test:uint = 0;
function get test():uint{ return _test; }
function set test(value:uint):void{ _test = value; }
// Direct access test.
function directTest(amt:int):Number
{
// Directly accessing the property.
var t:Number = getTimer();
for(var i:int = 0; i < amt; i++)
{
var temp:uint = _test;
_test = i;
}
return getTimer() - t;
}
// Getter/setter test.
function viaTest(amt:int):Number
{
// Via getter/setter.
var t:Number = getTimer();
for(var i:int = 0; i < amt; i++)
{
var temp:uint = test;
test = i;
}
return getTimer() - t;
}
A quick demonstration of how to use this:
trace("Direct: " + directTest(1000000));
trace("Getter/Setter: " + viaTest(1000000));
And some results that I got:
Amount Direct Get/Set
1000 0 0
5000 0 0
20,000 0 2
150,000 1 14
500,000 2 46
2,000,000 10 184
10,000,000 47 921
I always prefer to use getter and setter also into methods of the same class where they are declared (although I could use privare variables).
Getters and setters hide logic that is required when you have to set or get a class property, so you can modify "what-you-actually-do" inside your setter/getter without worry about impact in client methods.
They also avoid repetition of code.
But this is just my point of view... :)
Related
Why can't I compile this little piece of code ?
I'm overriding x and y in my class so that's why I need super.x.
public class SimpleSprite extends Sprite
{
override public function set x(value: Number): void
{
super.x -= 12;
//super.x = super.x - 12;
}
}
// or
public class SimpleSprite2 extends Sprite
{
public function get xx(): Number
{
return super.x;
}
public function set xx(value: Number): void
{
super.x = value;
}
public function SimpleSprite2()
{
xx -= 12;
super.x -= 12;
// Error: Syntax error: expecting semicolon before minusassign.
}
}
I know I can write super.x = super.x - 12; but im lazy and i dont want 2 look 4 these inconsistencies when i get hit by syntax errors im also very much accustomed to those shortcuts with -=
Looks like my IDE (FlashDevelop 4.2.3) bears the blame for this.
There's nothing syntactically wrong with what your doing. Your code works fine in my Flash Builder 4.7.
However, remember that instance.x -= value; is short for
instance.x = instance.x - value;
//ie.
instance.[set]x = instance.[get]x - value;
I mention this because of your top code:
override public function set x(value: Number): void
{
super.x -= 12;
//super.x = super.x - 12;
}
Makes me think you're trying to do something funny. Why are you decrementing in the set function?
If you need to have a seperate x value for a subclass, but can't change the interface (ie. you still want users to be able to say mySubClassInstance.x = 123.0;) do this:
public class DerivedSprite extends Sprite
{
protected var derivedX:Number;
public override function get x():Number
{
super.x = derivedX;
return derivedX;
}
public override function set x(value:Number):void
{
super.x = value;
derivedX = value;
}
public function DerivedSprite()
{
super();
derivedX = super.x;
}
}
I come to need a bit more info from my points, so I thought I'd add a previousX, previousY so that I can get a deltaX and deltaY. Now, this works fine if I make a simple self-contained class.
I think, however, that I'd like to extend the flash.geom.Point class to benefit from the other functions and calculations it offers.
So I extended Point and modified the x and y setters as I needed. When I compile, I get an error that these setters are not marked for override when they should be. So I override, but then I get an error that says these do not override any function.
Any clue where I screwed up?
Here is the class:
package net.jansensan.geom
{
import flash.geom.Point;
/**
* #author Mat Janson Blanchet
*/
public class UpdatablePoint extends Point
{
private var _previousX : Number = 0;
private var _previousY : Number = 0;
private var _deltaX : Number = 0;
private var _deltaY : Number = 0;
// ********************************************************************
// [ PUBLIC METHODS ]
// ********************************************************************
public function UpdatablePoint(x:Number=0, y:Number=0)
{
super(x, y);
}
override public function toString():String
{
return "(x=" + super.x + ", y=" + super.y + ", previousX=" +
_previousX + ", previousY=" + _previousY + ", deltaX=" +
_deltaX + ", deltaY=" + _deltaY + ")";
}
// ********************************************************************
// [ GETTERS / SETTERS ]
// ********************************************************************
override public function set x(x:Number):void
{
_previousX = super.x;
super.x = x;
_deltaX = super.x - _previousX;
}
override public function set y(y:Number):void
{
_previousY = super.y;
super.y = y;
_deltaY = super.y - _previousY;
}
public function get previousX():Number
{
return _previousX;
}
public function get previousY():Number
{
return _previousY;
}
public function get deltaX():Number
{
return _deltaX;
}
public function get deltaY():Number
{
return _deltaY;
}
}
}
The Point class isn't implemented using get/set-methods, rather it contains only public variables: public var x : Number and public var y : Number. See the documentation here.
Since you cannot override any public getters or setters you can't detect when anyone using your class is writing to these variables. What you can do is remove the extends Point and add a Point instance variable to your UpdatablePoint. Then change your getters and setters for x/y from super.[x/y] to myPointInstance.[x/y].
If you need to expose more functionality from the Point class, you could easily just wrap it. I.e. Say you want to use the 'equals'-method from Point, just create a copy of that method signature and make it's body contain: return myPointInstance.equals(p);
Point does not have public function set x or public function set y.
So you can't override them as they don't exist. Point is very low-level, my guess would be that Adobe didn't add these functions to avoid the increase in overload.
I am trying to create a basic functionality in AS3.
I have a class like this:
package tax
{
public class Calculator
{
public function Calculator()
{
}
private var grwage:Number;
private var taxes:Number;
private var superannuation:Number;
private var insurance:Number;
private var net:Number;
public function getGrwage():Number {
return grwage;
}
public function setGrwage(grwage:Number):void {
this.grwage = grwage;
}
public function getTaxes():Number {
return grwage;
}
public function setTaxes(taxes:Number):void {
this.taxes = grwage * 0.2;
}
public function getSup():Number {
return superannuation;
}
public function setSup(superannuation:Number):void {
this.superannuation = superannuation * 0.05;
}
public function getIns():Number {
return insurance;
}
public function setIns(insurance:Number):void {
this.insurance = insurance * 0.1;
}
public function getNet():Number {
return net;
}
public function setNet(net:Number):void {
this.net = grwage - taxes - superannuation - insurance;
}
}
}
Just some getters and setters.
And in my mxml file:
import tax.Calculator;
public var calculate:Calculator = new Calculator();
calculate.setGrwage(1000);
trace(calculate.getTaxes());
trace(calculate.getSup());
trace(calculate.getIns());
trace(calculate.getNet());
I get an error 1120 Access to undefinded property when I try to access calculate. Do you have any ideas?
Thanks.
I guess you're mixing up things a bit between getters and setters. If a variable depends on another, you have to write the calculation in its getter. This variable shouldn't exist as a private member and the accesses to it must always be done through the appropriate getter.
for example:
public function getNet():Number {
return getGrwage() - getTaxes() - getSup() - getIns();
}
So here, you only need one setter (setGrwage), you can remove the others ones and put the calculation in the getters.
Note that there is a more appropriate syntax for setters and getters in AS3.
class GetSet
{
private var privateProperty:String;
public function get publicAccess():String
{
return privateProperty;
}
public function set publicAccess(setValue:String):void
{
privateProperty = setValue;
}
}
There are multiple issues with your class. So lets redesign it
The main issue you had was you were not initiating the vars before you accessed them as they had a NULL value the flash player was throwing you that error.
As you can see in the constructor I set a default value of 0 so that they will never be NULL.
package tax {
public class Calculator{
private var _grwage:Number;
private var _taxes:Number;
private var _superannuation:Number;
private var _insurance:Number;
public function Calculator() {
this._grwage = 0;
this._taxes = 0;
this._superannuation = 0;
this._insurance = 0;
}
public function get grwage():Number {
return this._grwage;
}
public function set grwage(val:Number):void {
this._grwage = val;
}
public function get taxes():Number {
return this._taxes;
}
public function set taxes(val:Number):void {
this._taxes = val * 0.2;
}
public function get superannuation():Number {
return this._superannuation;
}
public function set superannuation(val:Number):void {
this._superannuation = val * 0.05;
}
public function get insurance():Number {
return this._insurance;
}
public function set insurance(val:Number):void {
this._insurance = val* 0.1;
}
public function get net():Number {
return this._grwage - this._taxes - this._superannuation - this._insurance;
}
}
}
import tax.Calculator;
public var calculate:Calculator = new Calculator();
//Now due to the fact we are using true setter/getter methods.
calculate.grwage = 1000;
trace( calculate.taxes); // should be 0 as we are defaulting to the initial value
trace( calculate.superannuation );// should be 0 as we are defaulting to the initial value
trace( calculate.insurance );// should be 0 as we are defaulting to the initial value
trace( calculate.net );// should be 1000 as we are defaulting to the initial values of everything but grwage
The answers here are all good, but they all miss the primary point:
You're trying to get your variables before you set them.
import tax.Calculator;
public var calculate:Calculator = new Calculator();
calculate.setGrwage(1000);
trace(calculate.getTaxes());
trace(calculate.getSup());
trace(calculate.getIns());
trace(calculate.getNet());
This will throw an error (due to the way you've set up your class), because you never called setSup(), setIns(), and setNet() before trying to use them.
While your class may not be written in the best way, it is syntactically sound.
Try calling each setter before your getter. I think you'll solve your issue.
If an AS3 method returns a reference to a complex type, is there any way to make that 'readonly', like how you can have const member functions in C++? An architecture I want to use calls for a class building itself from a passed template object... and really the template object should not be modifiable. I'm currently forced to add call-back enumerators and/or lots of extra accessor methods.
Flex has an ObjectUtil.clone() method that will make a deep copy. The copy will still by modifiable, but since it's a copy, the changes won't propagate back to the original.
The method is no complicated so if you're not using Flex, just add this to a util class:
public static function copy(value:Object):Object
{
var buffer:ByteArray = new ByteArray();
buffer.writeObject(value);
buffer.position = 0;
var result:Object = buffer.readObject();
return result;
}
There is no way to do that in AS3, there is Sam's way of doing it, but it still requires copying that object before you return it, depending on the complexity of that object, it can impact the performance.
Immutable interfaces are a near-equivillant to const-correctness. Here's an example:
interface CPoint {
function get x():Number;
function get y():Number;
}
class Point implements CPoint {
private var _x:Number;
private var _y:Number;
public function get x():Number { return _x; }
public function get y():Number { return _y; }
public function set x(val:Number) { _x = val; }
public function set y(val:Number) { _y = val; }
public function normalize():void {
var length:Number = Math.sqrt(_x*_x + _y*_y);
_x /= length;
_y /= length;
}
public function Point(x:Number, y:Number) {
_x = x; _y = y;
}
}
If you return a Point as a CPoint reference, then its fields cannot be altered. You can do an explicit cast to a Point from a CPoint to force access, but you can do the same thing with const casting in C++.
Unfortunately, AS3 doesn't support covariance like it should, so things get unnecessarily difficult for const sub-objects. For example, if you had a Line class that was made up of two points, you might want to say line.start.x = 47; if you have full access to the line, but allow reading of line.start.x through an immutable interface. You could do this if there was covariance, but instead you'll need to add separate get properties for mutable and immutable properties. So, you'd end up instead with line.cstart.x for reads from a CLine. Something like this:
interface CLine {
function get cstart():CPoint;
function get cend():CPoint;
}
class Line implements CLine {
private var _end:Point;
private var _start:Point;
public function get cend():CPoint { return _end; }
public function get cstart():CPoint { return _start; }
public function get end():Point { return _end; }
public function get start():Point { return _start; }
public function Line(x1:Number, y1:Number, x2:Number, y2:Number) {
_start = new Point(x1, y1);
_end = new Point(x2, y2);
}
}
I would create a flash.utils.proxy object. You could create a proxy object that has read only implementation of a child that is passed in.
Here is the documentation for creating a proxy object. http://livedocs.adobe.com/flash/9.0/ActionScriptLangRefV3/flash/utils/Proxy.html
Note: Proxy is pretty damn slow, since you'll be bypassing native object checking, and replacing it with a function call -- which when using a lot will be slow. I would do some simple performance testing first.
note: This is pseudo-code.
use namespace flash_proxy;
dynamic class ReadOnly extends flash.utils.Proxy {
private var target:Object;
public function ReadOnly(target:Object) {
this.target = target;
}
flash_proxy function getProperty(name:*):*
return target[name];
}
flash_proxy function setProperty(name:*, value:*):void
// throw an error or do nothing
}
}
You could then do:
var readOnly:ReadOnly = new ReadOnly(stage.loaderInfo.parameters);
readOnly.someparameter = 'newvalue';
trace(readOnly.someparameter); // should be old value
I have a number of value objects and I want to be able to create a function within it to trace out the properties and the values without specifying them directly. It will allow me to use the same code in all value objects as opposed to referring to variables within the value object. Ideally, I would like to replace the code in blogURLVars with this code.
Here's a sample value object
package items {
public class Blog {
private var _itemID:uint;
private var _blogTitle:String;
private var _blogText:String;
private var _blogCreated:String;
private var _blogCategory:String;
private var _blogFrontpage:Boolean;
public function Blog (itemID:uint,blogTitle:String,blogText:String,blogCategory:String,blogCreated:String,blogFrontpage:Boolean=false) {
_itemID = itemID;
_blogTitle = blogTitle;
_blogText = blogText;
_blogCreated = blogCreated;
_blogCategory = blogCategory;
_blogFrontpage = blogFrontpage;
}
public function get itemID():uint {
return _itemID;
}
public function get blogTitle():String {
return _blogTitle;
}
public function get blogText():String {
return _blogText;
}
public function get blogCategory():String {
return _blogCategory;
}
public function get blogCreated():String {
return _blogCreated;
}
public function get blogFrontpage():Boolean {
return _blogFrontpage;
}
public function toString():void {
}
public function blogURLVars():String {
var s:String;
s = "itemID="+ _itemID;
s += "blogTitle="+ _blogTitle;
s += "blogText="+ _blogText;
s += "blogCategory="+ _blogCategory;
s += "blogCreated="+ _blogCreated;
s += "blogFrontpage="+ _blogFrontpage;
return s;
}
}
}
DescrybeType could be of help here. I'm basing this answer in this other answer (you might want to check it out): Fastest way to get an Objects values in as3
Basically, the describeType function will let you inspect the public interface of your object. That means public variables, getter/setters and methods (plus some other info not relevant to your problem). So you get a list of all the getters and with that, return the names of said properties plus their actual values for a given object. Not that this is not exactly the same as your sample code, since this will not use the private variables, but rather will call the getters.
In code, this could be something like this (based on code in the linked question).
package {
import flash.net.URLVariables;
import flash.utils.describeType;
import flash.utils.getQualifiedClassName;
public class PropertiesHelper {
public function PropertiesHelper() {
}
private static var typePropertiesCache:Object = {};
public static function getPropertyNames(instance:Object):Array {
var className:String = getQualifiedClassName(instance);
if(typePropertiesCache[className]) {
return typePropertiesCache[className];
}
var typeDef:XML = describeType(instance);
trace(typeDef);
var props:Array = [];
for each(var prop:XML in typeDef.accessor.(#access == "readwrite" || #access == "readonly")) {
props.push(prop.#name);
}
return typePropertiesCache[className] = props;
}
public static function getNameValuePairs(instance:Object):URLVariables {
var props:Array = getPropertyNames(instance);
var vars:URLVariables = new URLVariables();
for each(var prop:String in props) {
vars[prop] = instance[prop];
}
return vars;
}
}
}
Use:
var blog:Blog = new Blog(1,"title&","text","cat","created");
var urlVars:URLVariables = PropertiesHelper.getNameValuePairs(blog);
trace(urlVars);
I'm using a URLVariables object since it seems that's what you want (though not actually what you blogURLVars method does), but you could change that in the getNameValuePairs method to suit your needs if necessary. An advantage of using a URLVariables object is that it handles the url-encoding for you automatically, so reserved characters such as &, =, etc, should not be a problem.