ios - 在快速关闭中返回 Void 和 () 之间的区别

Question

这些闭包有什么区别？

let closureA: () -> ()

和

let closureB: () -> Void

Answer 1

如果查看标题，您会发现 Void 是 () 的类型别名，

/// The empty tuple type.
///
/// This is the default return type of functions for which no explicit
/// return type is specified.
typealias Void = ()

您可以像这样使用 playground 来验证，

let a  = Void()
print(a) // prints  ()

更新

如果你想在头文件中看到 Void 的声明，在上面的代码中，像这样在 swift playground 或 xcode 编辑器中输入下面的代码，

  let a: Void  =  ()

然后，cmd + 单击上面表达式中的“Void”关键字，您将被带到头文件，您可以在其中实际看到 Void 的声明。

文档已更新，包含更多信息，如下所示，

/// The return type of functions that don't explicitly specify a return type;
/// an empty tuple (i.e., `()`).
///
/// When declaring a function or method, you don't need to specify a return
/// type if no value will be returned. However, the type of a function,
/// method, or closure always includes a return type, which is `Void` if
/// otherwise unspecified.
///
/// Use `Void` or an empty tuple as the return type when declaring a
/// closure, function, or method that doesn't return a value.
///
///     // No return type declared:
///     func logMessage(_ s: String) {
///         print("Message: \(s)")
///     }
///
///     let logger: (String) -> Void = logMessage
///     logger("This is a void function")
///     // Prints "Message: This is a void function"
public typealias Void = ()