实例方法
first(where:)
返回满足给定谓词的序列的第一个元素。
声明
func first(where predicate: (Self.Element) throws -> Bool) rethrows -> Self.Element?
返回值
满足 predicate
的序列的第一个元素,如果没有满足 predicate
的元素,则为 nil
。
参数
predicate
一个闭包,它将序列的一个元素作为其参数,并返回一个布尔值,指示该元素是否匹配。
详述
以下示例使用 first(where:)
方法在整数数组中查找第一个负数:
let numbers = [3, 7, 4, -2, 9, -6, 10, 1]
if let firstNegative = numbers.first(where: { $0 < 0 }) {
print("The first negative number is \(firstNegative).")
}
// Prints "The first negative number is -2."
可用版本
iOS 8.0+, iPadOS 8.0+, macOS 10.10+, Mac Catalyst 13.0+, tvOS 9.0+, watchOS 2.0+
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