More Monadical Optionals in Swift

Optional+Extension.swift

//  Copyright © 2020 Zack Sheppard. All rights reserved.
//  Available under the MIT License

/// A few Sequence/Monad-like functions added to Optional
extension Optional {
    /// Transform this optional into another type
    @inlinable public func map<T>(_ transform: (Wrapped) throws -> T) rethrows -> T? {
        if let inside = self {
            return try transform(inside)
        } else {
            return nil
        }
    }

    /// Transform this optional into another type, collapsing that type's optional nature with this one's
    @inlinable public func compactMap<T>(_ transform: (Wrapped) throws -> T?) rethrows -> T? {
        if let inside = self {
            return try transform(inside)
        } else {
            return nil
        }
    }

    /// Filter this optional using an include pass function.
    /// - Returns: `nil` if this is `nil` or if the `include` function returns `false` for the wrapped object.
    @inlinable public func filter(_ include: (Wrapped) throws -> Bool) rethrows -> Wrapped? {
        if let inside = self, try include(inside) {
            return inside
        } else {
            return nil
        }
    }
}