Add utilities/parallel_markers.hpp

Move logic from apply_context::unused_authorizations out to a header so
other code can use it.

The logic in question takes an array of data, and a parallel array of
"markers" (booleans, in this instance), and returns a range containing
only the data elements whose corresponding marker matches a provided
value (i.e. the boolean was true).

Stay tuned to see how else I use this code! ;)

libraries/chain/message_handling_contexts.cpp

@@ -4,11 +4,10 @@
 #include <eos/chain/key_value_object.hpp>
 #include <eos/chain/chain_controller.hpp>
 
+#include <eos/utilities/parallel_markers.hpp>
+
 #include <boost/algorithm/cxx11/all_of.hpp>
 #include <boost/range/algorithm/find_if.hpp>
-#include <boost/range/combine.hpp>
-#include <boost/range/adaptor/filtered.hpp>
-#include <boost/range/adaptor/transformed.hpp>
 
 namespace eos { namespace chain {
 
@@ -48,15 +47,7 @@ bool apply_context::all_authorizations_used() const {
 }
 
 vector<types::AccountPermission> apply_context::unused_authorizations() const {
-   auto RemoveUsed = boost::adaptors::filtered([](const auto& tuple) {
-      return !boost::get<0>(tuple);
-   });
-   auto ToPermission = boost::adaptors::transformed([](const auto& tuple) {
-      return boost::get<1>(tuple);
-   });
-
-   // zip the parallel arrays, filter out the used authorizations, and return just the permissions that are left
-   auto range = boost::combine(used_authorizations, msg.authorization) | RemoveUsed | ToPermission;
+   auto range = utilities::FilterDataByMarker(msg.authorization, used_authorizations, false);
    return {range.begin(), range.end()};
 }
 

libraries/utilities/include/eos/utilities/parallel_markers.hpp

+#pragma once
+
+#include <boost/range/combine.hpp>
+#include <boost/range/adaptor/filtered.hpp>
+#include <boost/range/adaptor/transformed.hpp>
+
+namespace eos { namespace utilities {
+
+/**
+ * @brief Return values in DataRange corresponding to matching Markers
+ *
+ * Takes two parallel ranges, a Data range containing data values, and a Marker range containing markers on the
+ * corresponding data values. Returns a new Data range containing only the values corresponding to markers which match
+ * markerValue
+ *
+ * For example:
+ * @code{.cpp}
+ * vector<char> data = {'A', 'B', 'C'};
+ * vector<bool> markers = {true, false, true};
+ * auto markedData = FilterDataByMarker(data, markers, true);
+ * // markedData contains {'A', 'C'}
+ * @endcode
+ */
+template<typename DataRange, typename MarkerRange, typename Marker>
+DataRange FilterDataByMarker(DataRange data, MarkerRange markers, const Marker& markerValue) {
+   auto RemoveMismatchedMarkers = boost::adaptors::filtered([&markerValue](const auto& tuple) {
+      return boost::get<0>(tuple) == markerValue;
+   });
+   auto ToData = boost::adaptors::transformed([](const auto& tuple) {
+      return boost::get<1>(tuple);
+   });
+
+   // Zip the ranges together, filter out data with markers that don't match, and return the data without the markers
+   auto range = boost::combine(markers, data) | RemoveMismatchedMarkers | ToData;
+   return {range.begin(), range.end()};
+}
+
+}} // namespace eos::utilities
+