Use the newly-added try_emplace() function, to work around Qt's
associative container's broken insert() behavior (which is
equivalent to STL's insert_or_assign()), forcing either a double
lookup:
auto it = c.find(key); // lookup 1
if (it == c.end())
c.insert(key, ~~~); // lookup 2
or the usual size-check trick:
const auto oldSize = c.size();
auto &e = c[key];
if (c.size() != oldSize) {
// newly inserted
onto any lookup-or-initialize-like code. try_emplace beats them
both in terms of efficiency and readability.
Pick-to: 6.3
Change-Id: I4c52d2f2d5175991db4931d29c688de125f5b032
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
66a183298a