arrays - Swift:按键引用数组元素

Question

我已经编写了自己的小函数来使用键在数组中查找元素。但我确信在 Swift 中有一个随时可用的实现，可以将它放在一行中。有什么提示吗？

func objectAtKey(array: [T], key: String) -> T? {
    for element in array {
        if element.name == key {
            return element
        }
    }
    return nil
}

我也知道函数 indexOf，但是它返回一个索引，我必须使用它来进行进一步的访问。我认为这比较慢:

let index = array.indexOf({$0.name == key})

Answer 1

在 Swift 3(Xcode 8，目前是 beta 6)中你可以这样做

if let el = array.first(where: { $0.name == key }) {
    // `el` is the first array element satisfying the condition.
    // ...
} else {
    // No array element satisfies the condition.
}

使用 Sequence 协议(protocol)的 first(where:) 方法:

/// Returns the first element of the sequence that satisfies the given
/// predicate or nil if no such element is found.
///
/// - Parameter predicate: A closure that takes an element of the
///   sequence as its argument and returns a Boolean value indicating
///   whether the element is a match.
/// - Returns: The first match or `nil` if there was no match.
public func first(where predicate: (Element) throws -> Bool) rethrows -> Element?