Understanding AS3 getDefinitionByName (for all eval maniacs)

Sometimes you may want to create a new class or DisplayObject only starting from its name. This is where something like an eval function would come into play, but we have to manage it in a different way with AS3.

Look at this movie:

Circles are four different objects called symbol1, symbol2, symbol3 and symbol4 and this is the script:

package {
	import flash.display.Sprite;
	public class Main extends Sprite {
		public function Main() {
			var s1:symbol1=new symbol1();
			addChild(s1);
			s1.x=95;
			s1.y=100;
			var s2:symbol2=new symbol2();
			addChild(s2);
			s2.x=245;
			s2.y=100;
			var s3:symbol3=new symbol3();
			addChild(s3);
			s3.x=395;
			s3.y=100;
			var s4:symbol4=new symbol4();
			addChild(s4);
			s4.x=545;
			s4.y=100;
		}
	}
}

Obviously it’s a bit unoptimized, just think about if we had a thousand objects. That’s when getDefinitionByName comes into play. It returns a reference to the class object of the class specified by the name parameter.

This means the same script can be written this way:

package {
	import flash.display.Sprite;
	import flash.utils.*
	public class Main extends Sprite {
		public function Main() {
			var symbolName:String;
			var symbolClass:Class;
			var s:Sprite;
			for (var i:int=1; i<=4; i++) {
				symbolName="symbol"+i;
				symbolClass=getDefinitionByName(symbolName) as Class;
				s=new symbolClass();
				addChild(s);
				s.x=95+150*(i-1);
				s.y=100;
			}
		}
	}
}

DisplayObjects names are passed as strings in getDefinitionByName method and created as generic classes that can be used anywhere in the movie.

If you want to see a real world example, cracks textures in my upcoming game have been made this way:

Starting from a random number I create the texture according to such number and the material name.

Something to keep in mind if you can't use anything similar to eval.

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214 GAME PROTOTYPES EXPLAINED WITH SOURCE CODE
// 1+2=3
// 100 rounds
// 10000000
// 2 Cars
// 2048
// A Blocky Christmas
// A Jumping Block
// A Life of Logic
// Angry Birds
// Angry Birds Space
// Artillery
// Astro-PANIC!
// Avoider
// Back to Square One
// Ball Game
// Ball vs Ball
// Ball: Revamped
// Balloon Invasion
// BallPusher
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// Bejeweled
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// Block it
// Blockage
// Bloons
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// Bombuzal
// Boom Dots
// Bouncing Ball
// Bouncing Ball 2
// Bouncy Light
// BoxHead
// Breakout
// Bricks
// Bubble Chaos
// Bubbles 2
// Card Game
// Castle Ramble
// Chronotron
// Circle Chain
// Circle Path
// Circle Race
// Circular endless runner
// Cirplosion
// CLOCKS - The Game
// Color Hit
// Color Jump
// ColorFill
// Columns
// Concentration
// Crossy Road
// Crush the Castle
// Cube Jump
// CubesOut
// Dash N Blast
// Dashy Panda
// Deflection
// Diamond Digger Saga
// Don't touch the spikes
// Dots
// Down The Mountain
// Drag and Match
// Draw Game
// Drop Wizard
// DROP'd
// Dudeski
// Dungeon Raid
// Educational Game
// Elasticity
// Endless Runner
// Erase Box
// Eskiv
// Farm Heroes Saga
// Filler
// Flappy Bird
// Fling
// Flipping Legend
// Floaty Light
// Fuse Ballz
// GearTaker
// Gem Sweeper
// Globe
// Goat Rider
// Gold Miner
// Grindstone
// GuessNext
// Helicopter
// Hero Emblems
// Hero Slide
// Hexagonal Tiles
// HookPod
// Hop Hop Hop Underwater
// Horizontal Endless Runner
// Hundreds
// Hungry Hero
// Hurry it's Christmas
// InkTd
// Iromeku
// Jet Set Willy
// Jigsaw Game
// Knife Hit
// Knightfall
// Legends of Runeterra
// Lep's World
// Line Rider
// Lumines
// Magick
// MagOrMin
// Mass Attack
// Math Game
// Maze
// Meeblings
// Memdot
// Metro Siberia Underground
// Mike Dangers
// Mikey Hooks
// Nano War
// Nodes
// o:anquan
// One Button Game
// One Tap RPG
// Ononmin
// Pacco
// Perfect Square!
// Perfectionism
// Phyballs
// Pixel Purge
// PixelField
// Planet Revenge
// Plants Vs Zombies
// Platform
// Platform game
// Plus+Plus
// Pocket Snap
// Poker
// Pool
// Pop the Lock
// Pop to Save
// Poux
// Pudi
// Pumpkin Story
// Puppet Bird
// Pyramids of Ra
// qomp
// Quick Switch
// Racing
// Radical
// Rebuild Chile
// Renju
// Rise Above
// Risky Road
// Roguelike
// Roly Poly
// Run Around
// Rush Hour
// SameGame
// SamePhysics
// Save the Totem
// Security
// Serious Scramblers
// Shrink it
// Sling
// Slingy
// Snowflakes
// Sokoban
// Space Checkers
// Space is Key
// Spellfall
// Spinny Gun
// Splitter
// Spring Ninja
// Sproing
// Stabilize!
// Stack
// Stick Hero
// String Avoider
// Stringy
// Sudoku
// Super Mario Bros
// Surfingers
// Survival Horror
// Talesworth Adventure
// Tetris
// The Impossible Line
// The Moops - Combos of Joy
// The Next Arrow
// Threes
// Tic Tac Toe
// Timberman
// Tiny Wings
// Tipsy Tower
// Toony
// Totem Destroyer
// Tower Defense
// Trick Shot
// Tunnelball
// Turn
// Turnellio
// TwinSpin
// vvvvvv
// Warp Shift
// Way of an Idea
// Whack a Creep
// Wheel of Fortune
// Where's my Water
// Wish Upon a Star
// Word Game
// Wordle
// Worms
// Yanga
// Yeah Bunny
// Zhed
// zNumbers