module data.list; public import data.model : NoteList; import std.typecons : Nullable; interface NoteListDataSource { NoteList[] getLists(string username); Nullable!NoteList getList(string username, ulong id); NoteList createNoteList(string username, string name, string description = null); void deleteNoteList(string username, ulong id); NoteList updateNoteList(string username, ulong id, NoteList newData); ulong countLists(string username); } static NoteListDataSource noteListDataSource; static this() { import data.impl.list; noteListDataSource = new SqliteNoteListDataSource(); }