I have the following code in a swift file:
我在swift文件中有以下代码:
func testDictionary(dict :Dictionary<String,AnyObject>) {
var str = ""
for var key in dict.keys {
str += key + ":" + dict[key]!.description + "\n"
}
self.alert("Dict", message: str)
}
The above code produces a warning on the user of var in the for loop, which is:
以上代码对for循环中的var用户发出警告:
Variable 'key' was never mutated; consider changing to 'let' constant
However when I change var to let I get the following error:
但是当我改变var让我得到以下错误:
'let' pattern cannot appear nested in an already immutable context
Why do I get a warning when the suggested correction is a compiler error?
当建议的更正是一个编译错误时，为什么会得到警告?
2 个解决方案
#1
21
Neither var nor let is needed in the statement. Type this:
语句中既不需要var，也不需要let。类型:
for key in dict.keys {
str += key + ":" + dict[key]!.description + "\n"
}
#2
0
I think the answer here is that the for-in loop by default provides a key that is already a constant. Therefore using the let keyword is redundant. When you used the var keyword, you were saying you wanted a variable key, but you never change it, therefore you don't need to use var.
我认为这里的答案是forin循环默认地提供了一个已经是常量的键。因此使用let关键字是多余的。当您使用var关键字时，您说您想要一个变量键，但是您从不更改它，因此您不需要使用var。
#1
21
Neither var nor let is needed in the statement. Type this:
语句中既不需要var，也不需要let。类型:
for key in dict.keys {
str += key + ":" + dict[key]!.description + "\n"
}
#2
0
I think the answer here is that the for-in loop by default provides a key that is already a constant. Therefore using the let keyword is redundant. When you used the var keyword, you were saying you wanted a variable key, but you never change it, therefore you don't need to use var.
我认为这里的答案是forin循环默认地提供了一个已经是常量的键。因此使用let关键字是多余的。当您使用var关键字时，您说您想要一个变量键，但是您从不更改它，因此您不需要使用var。