Kotlin 中的函数参数名称

Question

我在一些 Kotlin 示例中看到了下一个语法，其中参数名称在传递值之前设置:

LoginResult(success = LoggedInUserView(displayName = result.data.displayName))

上面的语法与下面的语法有什么区别？它只是视觉效果还是有某种目的？

LoginResult(LoggedInUserView(result.data.displayName))

Answer 1

根据the Kotlin Documentation :

When calling a function, you can name one or more of its arguments. This may be helpful when a function has a large number of arguments, and it's difficult to associate a value with an argument, especially if it's a boolean or null value.

When you use named arguments in a function call, you can freely change the order they are listed in, and if you want to use their default values you can just leave them out altogether.

本质上，当函数有很多参数时它们会很有帮助。例如，代替:

doSomething(true, true, true)

为了清楚起见，我们可以命名这些参数:

doSomething(
   first = true,
   second = true,
   third = true
)

编译后的代码是相同的，这只是为了让开发人员清楚起见。

另一个用例是，如果您愿意，您可以混合顺序:

doSomething(
    third = true,
    first = false,
    second = false
)

同样，生成的代码以相同的方式工作，这也是为了开发人员清楚。