https://lviv.dotnet.city/2010/09/%d0%bf%d0%b0%d1%82%d0%b5%d1%80%d0%bd-%d0%b2%d1%96%d0%b2%d1%82%d0%be%d1%80%d0%ba%d0%b0-6-%d1%84%d0%b0%d0%b1%d1%80%d0%b8%d1%87%d0%bd%d0%b8%d0%b9-%d0%bc%d0%b5%d1%82%d0%be%d0%b4-factory-method/