What to use

snippets.swift

// In Swift a method can be marked with rethrows keyword. It means that it throws an error only if one of its arguments throws an error.
 
func bar(callback: () throws -> Void) rethrows {
    try callback()
}

//using String to throw an error.

extension String: Error {}
func bar() throws {
    throw "Something went wrong!"
}

// Forced Unwrapping URLs

// Returns `URL` with guided fail
public enum SocketEndPoint: String {
    case events = "http://nowhere.com/events"
    case live = "http://nowhere.com/live"
    
    public var url: URL {
        guard let url = URL(string: self.rawValue) else {
            fatalError("Unconstructable URL: \(self.rawValue)")
        }
        return url
    }
}

// His initializer
fileprivate init() {
    self.eventSocket = WebSocket(url: SocketEndPoint.events.url))
    self.liveSocket = WebSocket(url: SocketEndPoint.live.url))
    self.eventSocket.delegate = self
    self.liveSocket.delegate = self
}

// I’d like to propose a new operator for optional assignment in Swift.
//The idea is that by using this operator (e.g. by doing a ?= b), the optional on the right would be assigned to the variable on the left only when it has something to assign (i.e. when it's not nil).
// The implementation could be something as follows:

/// Optional Assignment Operator
infix operator ?=: AssignmentPrecedence

func ?=<T>(left: inout T, right: T?) {
    if right != nil {
        left = right!
    }
}

func ?=<T>(left: inout T?, right: T?) {
    if right != nil {
        left = right
    }
}

/// A type that has an empty value representation, as opposed to `nil`.
public protocol EmptyValueRepresentable {
    /// Provide the empty value representation of the conforming type.
    static var emptyValue: Self { get }

    /// - returns: `true` if `self` is the empty value.
    var isEmpty: Bool { get }

    /// `nil` if `self` is the empty value, `self` otherwise.
    /// An appropriate default implementation is provided automatically.
    func nilIfEmpty() -> Self?
}

extension EmptyValueRepresentable {
    public func nilIfEmpty() -> Self? {
        return self.isEmpty ? nil : self
    }
}

extension Array: EmptyValueRepresentable {
    public static var emptyValue: [Element] { return [] }
}

extension Set: EmptyValueRepresentable {
    public static var emptyValue: Set<Element> { return Set() }
}

extension Dictionary: EmptyValueRepresentable {
    public static var emptyValue: Dictionary<Key, Value> { return [:] }
}

extension String: EmptyValueRepresentable {
    public static var emptyValue: String { return "" }
}

public extension Optional where Wrapped: EmptyValueRepresentable {
    /// If `self == nil` returns the empty value, otherwise returns the value.
    public func valueOrEmpty() -> Wrapped {
        switch self {
        case .some(let value):
            return value
        case .none:
            return Wrapped.emptyValue
        }
    }

    /// If `self == nil` returns the empty value, otherwise returns the result of
    /// mapping `transform` over the value.
    public func mapOrEmpty(_ transform: (Wrapped) -> Wrapped) -> Wrapped {
        switch self {
        case .some(let value):
            return transform(value)
        case .none:
            return Wrapped.emptyValue
        }
    }
}

//https://gist.github.com/riteshhgupta/358db2ed3b6968ef18880cb28bdb6963
extension Optional {
	// `then` function executes the closure if there is some value
	func then(_ handler: (Wrapped) -> Void) {
		switch self {
		case .some(let wrapped): return handler(wrapped)
		case .none: break
		}
	}
}

import Foundation

extension Optional 
{
    @discardableResult
    func ifSome(_ handler: (Wrapped) -> Void) -> Optional {
        switch self {
            case .some(let wrapped): handler(wrapped); return self
            case .none: return self
        }
    }
    @discardableResult
    func ifNone(_ handler: () -> Void) -> Optional {
        switch self {
            case .some: return self
            case .none(): handler(); return self
        }
    }
}

struct Person {
    let name: String
}

var p: Person? = Person(name: "Joe")
p.ifSome { print($0) }.ifNone { print("none") } // prints Person

p = nil
p.ifSome { print($0) }.ifNone { print("none") } // prints none

// https://oleb.net/blog/2016/12/optionals-string-interpolation/?utm_campaign=This%2BWeek%2Bin%2BSwift&utm_medium=email&utm_source=This_Week_in_Swift_114

infix operator ???: NilCoalescingPrecedence

public func ???<T>(optional: T?, defaultValue: @autoclosure () -> String) -> String {
    switch optional {
    case let value?: return String(describing: value)
    case nil: return defaultValue()
    }
}

public func ???<T>(optional: T?, defaultValue: @autoclosure () -> String) -> String {
    return optional.map { String(describing: $0) } ?? defaultValue()
}

var someValue: Int? = 5
print("The value is \(someValue ??? "unknown")")
// → "The value is 5"
someValue = nil
print("The value is \(someValue ??? "unknown")")
// → "The value is unknown"