Trying to get default value filling fixed.

I'm not sure it always works, but the idea is that this should
find the maximum size of all arrays resulting from a scraplang
struct query and make all entries the same length filling them
with:
1) the default value if one was given in scraplang
2) the value of the last entry in the array being filled
3) just empty values

It seems to work but I can't say I ran very extensive tests.
I'll test more in the future and fix as needed.

src/scraplang/apply.cpp

@@ -30,6 +30,8 @@
 #include <boost/variant/apply_visitor.hpp>
 #include <string_view>
 #include <list>
+#include <functional>
+#include <algorithm>
 
 namespace duck { namespace sl {
 #if defined(APPLY_VERBOSE)
@@ -48,6 +50,7 @@ namespace duck { namespace sl {
 			EntryNode
 		>>;
 		using MustacheEntryMap = std::map<std::string, MustacheEntry>;
+		typedef std::function<void(std::size_t)> FixLengthCommand;
 
 		struct EntryNode {
 			explicit EntryNode (const std::string_view& parName) :
@@ -106,6 +109,72 @@ namespace duck { namespace sl {
 			EntryNode& m_root;
 		};
 
+		class FillWithClonesVisitor : public boost::static_visitor<mstch::node&&> {
+		public:
+			explicit FillWithClonesVisitor (std::size_t exp_size) :
+				m_expected_size(exp_size)
+			{ }
+			virtual mstch::node&& operator()(mstch::array&& parOut) {
+				if (parOut.empty()) {
+					parOut.resize(m_expected_size);
+				}
+				else {
+					std::fill_n(
+						std::back_inserter(parOut),
+						std::max(m_expected_size, parOut.size()) - parOut.size(),
+						parOut.front()
+					);
+				}
+				m_retval = std::move(parOut);
+				return std::move(m_retval);
+			}
+
+			template <typename T>
+			mstch::node&& operator()(T&& parOut) {
+				mstch::array retval;
+				retval.reserve(m_expected_size);
+				retval.push_back(std::move(parOut));
+				return (*this)(std::move(retval));
+			}
+
+		protected:
+			mstch::node m_retval;
+			std::size_t m_expected_size;
+		};
+
+		class FillWithStringsVisitor : public FillWithClonesVisitor {
+		public:
+			FillWithStringsVisitor (const std::string& parVal, std::size_t exp_size) :
+				FillWithClonesVisitor(exp_size),
+				m_value(parVal)
+			{ }
+
+			mstch::node&& operator()(mstch::array&& parOut) override {
+				std::fill_n(
+					std::back_inserter(parOut),
+					std::max(m_expected_size, parOut.size()) - parOut.size(),
+					m_value.get()
+				);
+				m_retval = std::move(parOut);
+				return std::move(m_retval);
+			}
+
+			using FillWithClonesVisitor::operator();
+
+		private:
+			std::reference_wrapper<const std::string> m_value;
+		};
+
+		void fill_with_defaults (mstch::map& parMap, std::size_t parTotal, const std::string& parKey, const std::string& parDefault) {
+			FillWithStringsVisitor visitor(parDefault, parTotal);
+			parMap[parKey] = boost::apply_visitor(visitor, std::move(parMap[parKey]));
+		}
+
+		void fill_with_last_item_clones (mstch::map& parMap, std::size_t parTotal, const std::string& parKey) {
+			FillWithClonesVisitor visitor(parTotal);
+			parMap[parKey] = boost::apply_visitor(visitor, std::move(parMap[parKey]));
+		}
+
 		mstch::map to_mustache_dict_recursive (
 			const EntryNode& parNode,
 			std::string_view parSrc,
@@ -266,7 +335,7 @@ namespace duck { namespace sl {
 			return empty_retval;
 		}
 
-		std::size_t largest_array_size_in (mstch::map& parMap) {
+		std::size_t largest_array_size_in (const mstch::map& parMap) {
 			typedef ItemCountingVisitor ITC;
 			using boost::apply_visitor;
 
@@ -283,10 +352,13 @@ namespace duck { namespace sl {
 
 		void fill_with_xpaths (
 			mstch::map& parOut,
+			std::vector<FixLengthCommand>& parFixCommands,
 			const EntryNode& parNode,
 			std::string_view parSrc,
 			XPathRunner& parRunner
 		) {
+			using std::placeholders::_1;
+
 			for (const XPathElement* xpath : parNode.xpaths) {
 				assert(xpath);
 				std::cout << "Running query for \"" << xpath->name << "\"\n";
@@ -306,6 +378,11 @@ namespace duck { namespace sl {
 				else {
 					parOut[xpath->name] = std::string();
 				}
+
+				if (xpath->def_val)
+					parFixCommands.push_back(std::bind(&fill_with_defaults, std::ref(parOut), _1, std::cref(xpath->name), std::cref(*xpath->def_val)));
+				else
+					parFixCommands.push_back(std::bind(&fill_with_last_item_clones, std::ref(parOut), _1, std::cref(xpath->name)));
 			}
 		}
 
@@ -337,10 +414,16 @@ namespace duck { namespace sl {
 			XPathRunner& parRunner
 		) {
 			mstch::map retval;
+			std::vector<FixLengthCommand> fix_commands;
 
-			fill_with_xpaths(retval, parNode, parSrc, parRunner);
+			fill_with_xpaths(retval, fix_commands, parNode, parSrc, parRunner);
 			fill_with_structs(retval, parNode, parSrc, parRunner);
 
+			const std::size_t largest = largest_array_size_in(retval);
+			for (const auto& command : fix_commands) {
+				command(largest);
+			}
+
 			return retval;
 		}