As is customary for tag structs, make the default ctor explicit to avoid construction as '{}'. Make op== constexpr (drive-by: make it a hidden friend instead of a member function), and add op!= to C++17 builds, for symmetry. =delete the qHash() overload so it doesn't accidentally match some other overload. We should eventually also =delete equality, but atm, this breaks QSet::compareEquals, which calls QHash::op==, which (incorrectly) SFINAE's out for a non-equality-comparable QHashDummyValue mapped_type. Amends 5b7c3e31b538376f2b4733bd868b5875b504cdb3. Not picking back, as it's a rather isolated change with very little chance of creating conflicts going forward, but non-negligible chance of breaking something in older branches. Change-Id: I8125581c476f854ebe4f9ddc791d3ddce9f169d0 Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>