deprecate sound.group setter

flixel/sound/FlxSound.hx

@@ -114,9 +114,16 @@ class FlxSound extends FlxBasic
 	public var length(get, never):Float;
 
 	/**
-	 * The sound group this sound belongs to
+	 * The sound group this sound belongs to, can only be in one group.
+	 * NOTE: This setter is deprecated, use `group.add(sound)` or `group.remove(sound)`.
 	 */
-	public var group(default, set):FlxSoundGroup;
+	public var group(get, set):FlxSoundGroup;
+
+	/**
+	 * The sound group this sound belongs to. This is a temporary proxy for group, until it is removed
+	 */
+	@:allow(flixel.sound.FlxSoundGroup)
+	var _group:FlxSoundGroup;
 
 	/**
 	 * Whether or not this sound should loop.
@@ -707,24 +714,31 @@ class FlxSound extends FlxBasic
 	}
 	#end
 
-	function set_group(group:FlxSoundGroup):FlxSoundGroup
+	// Will be removed in a major version, and become a simple `(default,null)` var
+	inline function get_group():FlxSoundGroup
 	{
-		if (this.group != group)
+		return _group;
+	}
+
+	@:deprecated("sound.group = myGroup is deprecated, use myGroup.add(sound)") // 5.7.0
+	function set_group(value:FlxSoundGroup):FlxSoundGroup
+	{
+		if (_group != value)
 		{
-			var oldGroup:FlxSoundGroup = this.group;
+			final oldGroup = _group;
 
 			// New group must be set before removing sound to prevent infinite recursion
-			this.group = group;
+			_group = value;
 
 			if (oldGroup != null)
 				oldGroup.remove(this);
 
-			if (group != null)
-				group.add(this);
-				
+			if (value != null)
+				value.add(this);
+
 			updateTransform();
 		}
-		return group;
+		return value;
 	}
 
 	inline function get_playing():Bool

flixel/sound/FlxSoundGroup.hx

@@ -25,16 +25,20 @@ class FlxSoundGroup
 	}
 
 	/**
-	 * Add a sound to this group
+	 * Add a sound to this group, will remove the sound from any group it is currently in
 	 * @param	sound The sound to add to this group
 	 * @return True if sound was successfully added, false otherwise
 	 */
 	public function add(sound:FlxSound):Bool
 	{
-		if (sounds.indexOf(sound) < 0)
+		if (!sounds.contains(sound))
 		{
+			if (sound._group != null)
+				sound._group.sounds.remove(sound);
+
 			sounds.push(sound);
-			sound.group = this;
+			sound._group = this;
+			sound.updateTransform();
 			return true;
 		}
 		return false;
@@ -47,10 +51,12 @@ class FlxSoundGroup
 	 */
 	public function remove(sound:FlxSound):Bool
 	{
-		if (sounds.indexOf(sound) >= 0)
+		if (sounds.contains(sound))
 		{
-			sound.group = null;
-			return sounds.remove(sound);
+			sound._group = null;
+			sounds.remove(sound);
+			sound.updateTransform();
+			return true;
 		}
 		return false;
 	}

flixel/system/frontEnds/SoundFrontEnd.hx

@@ -106,6 +106,9 @@ class SoundFrontEnd
 	 */
 	public function playMusic(embeddedMusic:FlxSoundAsset, volume = 1.0, looped = true, ?group:FlxSoundGroup):Void
 	{
+		if (group == null)
+			group = defaultMusicGroup;
+
 		if (music == null)
 		{
 			music = new FlxSound();
@@ -114,11 +117,11 @@ class SoundFrontEnd
 		{
 			music.stop();
 		}
-
+		
 		music.loadEmbedded(embeddedMusic, looped);
 		music.volume = volume;
 		music.persist = true;
-		music.group = (group == null) ? defaultMusicGroup : group;
+		group.add(music);
 		music.play();
 	}
 
@@ -180,14 +183,15 @@ class SoundFrontEnd
 
 	function loadHelper(sound:FlxSound, volume:Float, group:FlxSoundGroup, autoPlay = false):FlxSound
 	{
+		if (group == null)
+			group = defaultSoundGroup;
+
 		sound.volume = volume;
-
+		group.add(sound);
+
 		if (autoPlay)
-		{
 			sound.play();
-		}
-
-		sound.group = (group == null) ? defaultSoundGroup : group;
+
 		return sound;
 	}