Just some utility functions for when you are working inside a throwing function

ThrowingUtils.swift

//
//  ThrowingUtils.swift
//
//  Created by Cristián Arenas Ulloa on 1/13/17.
//  WTFPLv2
//

// Usage example: try maybeValue.unwrapped()
extension Optional {
    func unwrapped() throws -> Wrapped {
        guard let unwrapped = self else {
            throw UnwrappingError()
        }
        return unwrapped
    }
}
struct UnwrappingError: Error {}

// Usage example: try cast(anyValue) as [String: Any]
func cast<T, U> (_ input: T) throws -> U {
    guard let output = input as? U else {
        throw CastingError(
            element: String(describing: type(of: input)),
            from: String(describing: T.self),
            to: String(describing: U.self)
        )
    }
    return output
}
struct CastingError: Error {
    let element: String
    let from: String
    let to: String
    
    var localizedDescription: String {
        return "CastingError: couldn't cast element of type \(element) from \(from) to \(to)"
    }
}