Macro trick

    private static var _modulesArray : Array<String> = null;
    public static var modulesArray(get, null) : Array<String>;

    public static function get_modulesArray() : Array<String>
    {
        if (_modulesArray == null)
        {
            _modulesArray = new Array<String>();
            importConfig();
        }
        return _modulesArray;
    }

    public static function fillArray()
    {
        _modulesArray.push("File 1");
        Sys.println("Should be printed once");
    }

    private static var cached : Expr = null;
    macro public static function importConfig()
    {
        if (_modulesArray == null)
            _modulesArray = new Array<String>();
        if (cached != null)
            return cached;
        fillArray();
        cached = Context.makeExpr("Awesome config", Context.currentPos());
        return cached;
    }