Checks whether a function declaration has parameters that are
top level const.
const values in declarations do not affect the signature of a
function, so they should not be put there.
This method allows to determine if a feature source has content or not
(or maybe).
This method works for "generator" sources as well as for "collection"
sources.
Collection sources like QgsVectorDataProvider which allow to easily and
in a cheap way determine if features are available can return
FeaturesAvailable or NoFeaturesAvailable, generators will return
FeaturesMaybeAvailable.
QgsVectorDataProvider also implements an empty() method.
in a layer
This is incredibly inefficient, because selectedFeatures() actually
fetches a full copy of all selected features (including all
attributes and geometry). Instead use selectedFeatureIds(), which
is just a list of numbers.
Add warning note to docs cautioning against this practice.
Fixes massive ui lockup when right clicking on a layer with
selected features in the layer tree
