Since Qt::DayOfWeek has such a limited range, it doesn't really make sense to use it as a key in a QMap, which is optimized for much larger key spaces. Replace by a C array of the value type, and, since the value type in question (QTextCharFormat) doesn't have an invalid state, use a bool array to track whether any of the seven possible keys has been inserted. Wrap that in a small helper class which provides only the subset of QMap API that QCalendarModel needs. Saves 1352 bytes of text size on optimized GCC AMD64 builds. Change-Id: Ie51390825d5933739659c4ea8e8da0af68577a9d Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>