Optional Map 和flatMap

gistfile1.txt

https://github.com/apple/swift/blob/master/stdlib/public/core/Optional.swift

@_inlineable
public func map<U>(_ transform: (Wrapped) throws -> U) rethrows -> U? {
    switch self {
    case .some(let y):
        return .some(try transform(y))
    case .none:
        return .none
    }
}

@_inlineable
public func flatMap<U>(_ transform: (Wrapped) throws -> U?) rethrows -> U? {
    switch self {
    case .some(let y):
        return try transform(y)
    case .none:
        return .none
    }
}