class ARandom{
    var number: Int = 0
    var text: String
}

stored property "text" without initial value prevents synthesized initializers

>使文本可选.

var text：String？
>给文本一个默认值

var text：String =“”
>在ARandom的初始化程序中给文本一个值

init(){text =“”}

发生这种情况的原因是您将文本定义为String.它不是可选的.基本上你说的是它总是一个String,永远​​不会是零.

使用您当前的代码,如果您创建了一个新的实例的ARandom,文本将没有价值 – 如果文本不可选,那是不可能的

苹果的文档可能会解释一下好一点

Classes and structures must set all of their stored properties to an
appropriate initial value by the time an instance of that class or
structure is created. Stored properties cannot be left in an
indeterminate state.

You can set an initial value for a stored property within an initializer,or by assigning a default property value as part of the property’s definition.