Swift函数中可选泛型参数的默认值

Is it possible to give an optional generic parameter a default value?

是否可以为可选的通用参数提供默认值？

I'm trying to do something like this:

我正在尝试做这样的事情：

func addChannel<T>(name: String, data: T? = nil) -> Channel {

}

let myChannel = addChannel("myChannelName")

But I'm getting an error saying

但是我说错了

Argument for generic parameter 'T' could not be inferred

无法推断出泛型参数“T”的参数

Is it just a case of what I'm trying to do being impossible?

这只是我想要做的事情的一个例子吗？

1 个解决方案

#1

It's impossible in the way you've done it. Given just the code above, what type is T? The compiler, as it says, can't figure it out (neither can I, and I assume you couldn't either because the data's not there).

你完成它的方式是不可能的。只给出上面的代码，T是什么类型的？正如它所说的那样，编译器无法弄明白（我也不能，而且我认为你也不能，因为数据不存在）。

The solution to the specific question is to overload rather than use defaults:

特定问题的解决方案是重载而不是使用默认值：

func addChannel<T>(name: String, data: T?) -> Channel { ... }

func addChannel(name: String) -> Channel { ... }

let myChannel = addChannel("myChannelName")

But it raises the question of what you're doing here. You would think that Channel should be Channel<T>. Otherwise, what are you doing with data? Without resorting to Any (which you should strongly avoid), it's hard to see how your function can do anything but ignore data.

但它提出了你在这里做什么的问题。你会认为Channel应该是Channel 。否则，你在做什么数据？如果不诉诸Any（你应该强烈避免），很难看出你的函数除了忽略数据之外什么都可以做。

With Channel<T> you can just use a default, but you'd have to provide the type:

使用Channel ，您可以使用默认值，但您必须提供以下类型：

func addChannel<T>(name: String, data: T? = nil) -> Channel<T> { ... }
let myChannel: Channel<Int> = addChannel("myChannelName")

Otherwise the compiler wouldn't know what kind of channel you're making.

否则，编译器不会知道您正在制作什么类型的频道。

#1