Extension that lets you require an optional to be non-nil, or throw an error (which is customizable)

Optional+Require.swift

extension Optional {
    struct RequireError: Error, CustomStringConvertible {
        var description: String {
            return "Required optional value was nil"
        }
    }

    func require(orThrow errorClosure: @autoclosure () -> Error = RequireError()) throws -> Wrapped {
        switch self {
        case .some(let value):
            return value
        case .none:
            throw errorClosure()
        }
    }
}

// Usage:

let value = try myOptional.require()
let value = try myOptional.require(orThrow: MyError.invalidValue)