In Qt 6, QMap is just a shared pointer to a std::map. QMimeBinaryProvider::m_mimetypeExtra is never copied, though, so the implicit sharing that QMap adds on top of std::map is useless. Use the underlying std::map directly. Yes, the std::map API is a bit raw around the edges (std::pair value_type), but we're professionals here. Saves more than 1.7KiB in TEXT size on optimized AMD64 GCC 11 C++20 Linux builds. As a drive-by, cut out the insertIt temporary, too, and assign directly to `it`. Change-Id: If3fd98a7e7017909d00b8725f8c252b19459d5b6 Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io> Reviewed-by: David Faure <david.faure@kdab.com>