Fix operator checks for containers whose value_type equals themselves. It does not make sense to recurse on value_type in that case. Thanks to std::disjunction having short-circuiting semantics, we can avoid that issue by checking first whether T is T::value_type. As a drive-by, check for value_type typedef before checking for begin/end in is_container. This works around an issue in gcc <= 8.1, which fails to correctly SFINAE the case where begin and end are private methods. Pick-to: 6.0 6.1 Fixes: QTBUG-89456 Change-Id: I27305a7cfe050f13a279c07f00bc229c01daa25b Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>