variables - Swift 中的多变量赋值

Question

如何使用 Swift 在一行中分配多个变量？

    var blah = 0
    var blah2 = 2

    blah = blah2 = 3  // Doesn't work???

Answer 1

你没有。

这是一种语言功能，可防止赋值返回值时出现标准的不良副作用，如 described in the Swift book :

Unlike the assignment operator in C and Objective-C, the assignment operator in Swift does not itself return a value. The following statement is not valid:

   if x = y {
       // this is not valid, because x = y does not return a value
   }

This feature prevents the assignment operator (=) from being used by accident when the equal to operator (==) is actually intended. By making if x = y invalid, Swift helps you to avoid these kinds of errors in your code.

因此，这有助于防止这种极其常见的错误。虽然这种错误可以在其他语言中减少——例如，通过使用 Yoda conditions ——Swift 的设计师显然决定最好在语言层面确保你不会搬起石头砸自己的脚。但这确实意味着您不能使用:

blah = blah2 = 3

如果您迫切希望在一行中进行赋值，您可以使用元组语法，但您仍然必须专门为每个值赋值:

(blah, blah2) = (3, 3)

...我不会推荐它。虽然一开始可能会觉得不方便，但在我看来，将整个内容键入是最好的方法:

blah = 3
blah2 = 3