类定义中的可选变量 [英] optional variable in class definition

问题描述

类定义中的可选选项

我有一个"mastermodel"，我的大多数模型都从"mastermodel"继承而来，因此它们可以具有配置常量

I have a 'mastermodel' from which most of my models inherit so they can have the configuration constants

class MasterModel {

    static let apiKey = (drop.config["app","thinx-api-key"]?.string)!
    static let baseURL = (drop.config["app","base-URL"]?.string )!

}

请注意，力解开了:( 在这种情况下，这并不是一个很大的问题，因为如果没有这些常量，程序将无法启动，但是无论如何，我还是想清理它.

Notice the force unwraps :( In this case it's not really a huge problem as the program won't start without these constants but I'd like to clean this up anyway.

guard语句仅允许在函数中使用，而不能在类定义中使用.用错误陷阱定义那些常量的正确方法是什么

guard statements are only allowed in functions, not in the class definition. What is the proper way to define those constants with error trapping

推荐答案

您可以为它们分配计算闭包以检测配置错误

You could assign them with a computed closure to detect the configuration error

class MasterModel 
{

  static let apiKey:String  = { 
     if let result = drop.config["app","thinx-api-key"]?.string 
     { return result }
     print("MasterModel.apiKey error, missing app/thinx-api-key")
     return ""
  }()  // the () here makes the closure execute and return the value

  // ...
}

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