new (maxlen:Int)
@:value(new Map<String,K>())data:Map<String, K> = new Map<String,K>()
@:value(new Array<String>())idx:Array<String> = new Array<String>()
maxlen:Int
get (id:String):Null<K>
iterator ():Iterator<K>
remove (id:String):Void
set (id:String, val:K):Void