Added a swap function to FlxArrayUtil

[UncertainProd]

This pr adds a simple swap function to FlxArrayUtil, which should be useful for re-ordering sprites like this:

layers.mp4

The code:

package;

import flixel.FlxG;
import flixel.FlxSprite;
import flixel.FlxState;
import flixel.text.FlxText;
import flixel.util.FlxArrayUtil;
import flixel.util.FlxColor;

class PlayState extends FlxState
{
	var card1:FlxSprite;
	var card2:FlxSprite;
	var helpText:FlxText;

	override public function create()
	{
		super.create();
		card1 = new FlxSprite().makeGraphic(100, 100, FlxColor.RED);
		card1.screenCenter();
		card1.x -= 20;

		card2 = new FlxSprite().makeGraphic(100, 100, FlxColor.YELLOW);
		card2.screenCenter();
		card2.x += 20;
		card2.y += 20;

		helpText = new FlxText(0, FlxG.height - 20, 0, 'Press ENTER to toggle which card is at the front');
		helpText.setFormat(null, 12, FlxColor.BLACK);
		helpText.screenCenter(X);
		add(helpText);

		FlxG.camera.bgColor = FlxColor.WHITE;
		add(card1);
		add(card2);
	}

	override public function update(elapsed:Float)
	{
		super.update(elapsed);
		if (FlxG.keys.justPressed.ENTER)
		{
			FlxArrayUtil.swap(members, members.indexOf(card1), members.indexOf(card2));
		}
	}
}

[Geokureli]

just in case you're unaware, FlxArrayUtil is meant to be used via static extension, or by adding using flixel.util.FlxArrayUtil to your imports. by adding a using statement to your example, you could replace

FlxArrayUtil.swap(members, members.indexOf(card1), members.indexOf(card2));

with a simpler line of:

members.swap(members.indexOf(card1), members.indexOf(card2));

[Geokureli]

1. I think your example illustrates that there should also be a way to swap elements of an array based on references to those elements rather than their indices. I would call that swap, and this should be swapIndices or swapByIndex. example:

public static function swap<T>(array:Array<T>, item1:T, item2:T):Array<T>
{
	return swapIndices(array, array.indexOf(item1), array.indexOf(item2));
}

public static function swapIndices<T>(array:Array<T>, index1:Int, index2:Int):Array<T>
{
	// ...
}

2. All new features in this class should have unit tests, in FlxArrayUtilTest.hx. Normally I add these, but this should be pretty easy, I'm the busiest I'll ever be, and you seem to know what your doing.

Check out the unit test readme.md. if you need help testing, let me know.

note that you can do things like:

Assert.isTrue([0, 1, 2, 3, 4, 5].swap(2, 4).equals([0, 1, 5, 3, 4, 2]));

[UncertainProd]

I think your example illustrates that there should also be a way to swap elements of an array based on references to those elements rather than their indices. I would call that swap, and this should be swapIndices or swapByIndex

swapByIndex sounds good, I've added functions for swapping based on index and based on the element itself, and added a safe version of them as well which will validate the input elements/indices

All new features in this class should have unit tests, in FlxArrayUtilTest.hx.

I've added in some tests as well. Using haxe test-cpp.hxml on my machine works for me but for some reason test-web.hxml shows an error saying 'ERROR: Local results server appeared to hang so test reporting was cancelled.', maybe it's because I don't have flash installed?

[JOEpapatsk]

just in case you're unaware, FlxArrayUtil is meant to be used via static extension, or by adding using flixel.util.FlxArrayUtil to your imports. by adding a using statement to your example, you could replace

FlxArrayUtil.swap(members, members.indexOf(card1), members.indexOf(card2));

with a simpler line of:

members.swap(members.indexOf(card1), members.indexOf(card2));

What do you mean adding to your imports? Do you mean adding "using bla.bla.Bla" to the playstate class??

[Geokureli]

What do you mean adding to your imports? Do you mean adding "using bla.bla.Bla" to the playstate class??

yeah I mean adding a using statement at the top of the file (where the imports go), like so:
https://github.com/HaxeFlixel/flixel/blob/dev/tests/unit/src/flixel/util/FlxArrayUtilTest.hx#L5

allowing you to use these methods as static extensions rather than static methods, like so:
https://github.com/HaxeFlixel/flixel/blob/dev/tests/unit/src/flixel/util/FlxArrayUtilTest.hx#L88