Question

我编写了自己的小函数，使用键在数组中查找元素。但我确信在Swift中有一个可以使用的实现来将它放在一行中。任何提示？

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，但这返回一个索引，我必须用于进一步访问。我认为这个比较慢：

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

Answer 1

在Swift 3（Xcode 8，目前是测试版6）中你可以做到

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first(where:)协议的Sequence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?

Answer 2

我认为这里最好的解决方案是使用indexOf和Predicate编写的代码。我会这样写的：

let array = ["Foo", "Bar", "Test"]
if let i = array.indexOf({$0 == "Foo"}) {
     print(array[i])
}

如果您需要，则处理该值是否存在。

Answer 3

试试这个：

let element = array.filter{ $0.name == key }.first

Swift：按键引用数组元素

3 个答案: