php const常量 不能使用字符串連接符.鏈接

class jdpay extends pay {



    const BASE_URL = "https://mapi.jdpay.com/npp10/";
    

    private $agreement_sign_url = self::BASE_URL . "agreement_sign"; //簽約請求的url get訪問
    private $agreement_cancel_url = self::BASE_URL . "agreement_cancel"; //解約請求
    private $agreement_pay_url = self::BASE_URL . "agreement_pay"; //支付請求
    private $account_query_url = self::BASE_URL . "account_query"; //余額查詢請求
}

 這個問題在php5.6以及以上的版本不是問題， 不然會報

syntax error, unexpected '.', expecting ',' or ';' 這樣的錯誤

呵呵，就項目沒辦法，只能按老辦法寫了