在Swift中,为什么以下代码会产生错误:错误:'Cannot use mutating member on immutable value: function call returns'var url: URL=URL(string: "string a")!url.appendPathComponent(“string b")
('/reportpeta/{filterperiode}','PetaReportController@getProvinsi');{{ Form::open(array('url' => url('/reportpeta/'),'method' => 'get')) }}{{!!控制器
public function getProvinsi(