ios 在 Swift 中 if let 赋值中 where 的使用
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Usage of where in if let assignment in Swift
提问by Fabrizio Bartolomucci
The Swift documentation at page 61 of the Swift manual hints to the possibility of using whereto join an optional binding with a regular condition. Yet when I do it I have a warning suggesting me to substitute the wherewith a comma like in the following piece of code:
Swift 手册第 61 页的 Swift 文档提示了使用where常规条件连接可选绑定的可能性。然而，当我这样做时，我有一个警告，建议我where用逗号替换，如下面的代码所示：
if let geocodingError = error as? NSError where geocodingError.code == 2
采纳答案by Alex
Example with two conditions
具有两个条件的示例
if let x = y, let a = b, a == x && !x.isEmpty {
回答by Grimxn
In Swift 3 this syntax has changed.
在 Swift 3 中，此语法已更改。
What was
什么是
if let x = y, a = b where a == x {
if let x = y, a = b where a == x {
Is now
就是现在
if let x = y, let a = b, a == x {
if let x = y, let a = b, a == x {
The justification is that each sub-clause of the if ... {is now an independent boolean test.
理由是每个子条款if ... {现在都是一个独立的布尔测试。
See the Xcode Release notes& the Swift Evolution proposalfor more info about this change.
有关此更改的更多信息，请参阅 Xcode发行说明和Swift Evolution 提案。
回答by luhuiya
In xcode 9
在 xcode 9
if let str = textField.text as String!, !str.isEmpty
{
params[key] = str
TextFieldHelper.setup(textField: textField)
}
else
{
TextFieldHelper.error(textField: textField)
}
