QPermission: replace T data<T>() with std::optional<T> value<T>()

As discussed in API review, the default-constructed T() returned from
a mismatched data<T>() call is indistinguishable from a real T with
default state.

To make them distinguishable, return optional<T>. Call the new
function value<T>(), mimicking QVariant::value<T>(), and suggested in
API review, because data() is usually used to return raw pointers, not
values.

Remove the qWarning() on requestedType and actualType mismatch, as the
new function can be used in std::get_if/dynamic_cast-like if-then-else
chains, in which failure is part of the normal operation, and a
warning message misplaced:

  if (auto loc = perm.value<QLocationPermission>())
     ~~~ use *loc ~~~
  else if (auto con = perm.value<QContactsPermission>())
     ~~~ use *con ~~~
  ~~~ etc ~~~

Pick-to: 6.5
Change-Id: I799a58e930307323ebce8f9ac50a42455e9c017f
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

0 files changed, 0 insertions, 0 deletions