We did this for Dates and Data specifically because they are 1. Incredibly common types, which are likely to have the same representation across your entire payload, because 2. Specific format requirements are likely controlled by whatever software is running on a server, and for those very integral types, the server is likely opinionated/has specific requirements いまいちよくわからない「DataとDateに特別にstrategyが許されるのは、全payloadでサーバの統制の元、同じ表現が使われがちだから」って意味であってますか？であれば、それはstrategyではなく、init(from:)の決め打ち実装をなくしてユーザーにextensionで書かせるべきなのでは