“导入UIKit”导致了双对int的转换错误。为什么?

I'm a Swift beginner and I have a question.

我是一个快速的初学者，我有一个问题。

I created a new playground file in Xcode6-Beta3 , and erased
all default snippets generated automatically. And I wrote following
one line only,

我在Xcode6-Beta3中创建了一个新的游乐场文件，并删除了自动生成的所有默认代码片段。我只写了一行，

var x:Int = (1.234 as Int)

And then, this line caused a compile error with message saying that

然后，这一行产生了一个编译错误，消息是这样的

Playground execution failed: 
error: <EXPR>:1:20: error: 
'Double' is not convertible to 
'Int'
var x:Int = (1.234 as Int)
               ^

in the Console Output. I can understand this error because 1.234 can not be casted as Int.

在控制台输出。我可以理解这个错误，因为1.234不能被转换为Int。

Next, I added one more line import UIKit before var x:Int = (1.234 as Int),
so the codes were following:

接下来，在var x:Int =(1.234作为Int)之前，我又添加了一个行导入UIKit，所以代码如下:

import UIKit

var x:Int = (1.234 as Int)

Then, the error message above disappeared. But I can't understand
the reason that adding import UIKit caused disappearing
the error message claiming that
'Double' is not convertible to 'Int'
above.

然后，上面的错误消息消失了。但是我不能理解为什么添加导入UIKit导致了错误信息的消失，声称“Double”不能转换到上面的“Int”。

Please teach me this reason or some references to understand about it.

请告诉我这个原因或一些参考资料来了解它。

Regards.

的问候。

1 个解决方案

#1

The compiler will always seek a way to make your code compiling as possible as it can. With import UIKit, your code is something equivalent to

编译器总是会寻找一种方法使您的代码尽可能地进行编译。使用导入UIKit，你的代码是等价的

var _x = 1.234 as NSNumber
var x:Int = (_x as Int)

The compiler can turn to NSNumber when have UIKit imported.

当有UIKit导入时，编译器可以转到NSNumber。

#1