Some convenience methods using Mirror to build a nice custom debugDescription easily

Mirror+DebugDescription.swift

extension Mirror {
    /// Use this to help you implement a custom debugDescription listing all properties of your instances
    ///
    /// - Parameters:
    ///   - subject: The instance for which to return the description.
    ///
    /// Example usage:
    ///
    ///       extension MyType: CustomDebugStringConvertible {
    ///         var debugDescription: String {
    ///           return Mirror.debugDescription(self)
    ///         }
    ///       }
    ///
    /// - Note: This will use a `Mirror` to extract the subject's type and list of properties
    ///         to include in the description
    ///
    static func debugDescription(_ subject: Any) -> String {
        let mirror = Mirror(reflecting: subject)
        return self.debugDescription(type: mirror.subjectType, children: Array(mirror.children))
    }

    /// Use this to help you implement a custom debugDescription listing custom properties of your instance
    ///
    /// - Parameters:
    ///   - type: The type for which to print the name of in the description
    ///   - properties: The list of custom properties to include in the description
    ///
    /// Example usage:
    ///
    ///       extension MyType: CustomDebugStringConvertible {
    ///           var debugDescription: String {
    ///               return Mirror.debugDescription(type(of: self), [
    ///                   "name": name,
    ///                   "color": color,
    ///                   "ownerName": owner?.name as Any
    ///               ])
    ///           }
    ///       }
    ///
    static func debugDescription(_ type: Any.Type,
                                 _ properties: DictionaryLiteral<String?, Any> = [:]) -> String {
        let children = properties.map({ (label: $0.key, value: $0.value) })
        return self.debugDescription(type: type, children: children)
    }

    private static func debugDescription(type: Any.Type, children: [Mirror.Child]) -> String {
        let props = children.map { (prop: Mirror.Child) -> String in
            let value = String(describing: prop.value)
            // for values on multiple lines, also add indentation to all lines except the first
            let desc = value.replacingOccurrences(of: "\n", with: "\n  ")
            return "  \(prop.label ?? "-"): \(desc)"
        }
        return "\(type)(\n\(props.joined(separator: ",\n"))\n)"
    }
}