From 5bfeeb70c6a7ed6ccda0576dc39050eb4240434f Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Mon, 20 Mar 2023 19:32:26 +0000
Subject: Lazy initialisation of SelectionPtr in persistValue

Always needed for write phase, but only need on read if their's a name match.
---
 lib/persistence.cpp | 22 ++++++++++++++--------
 lib/persistence.h   | 13 ++++++++-----
 2 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/lib/persistence.cpp b/lib/persistence.cpp
index 06e40c7..e22d74d 100644
--- a/lib/persistence.cpp
+++ b/lib/persistence.cpp
@@ -48,10 +48,15 @@ namespace Persistence {
 
 	PersistenceSelect::PersistenceSelect(const std::string & n) : name {n} { }
 
-	PersistenceStore::NameAction
-	PersistenceSelect::setName(const std::string_view key, const Selection &)
+	PersistenceStore::NameActionSelection
+	PersistenceSelect::setName(const std::string_view key, SelectionFactory && factory)
 	{
-		return (key == name) ? NameAction::Push : NameAction::Ignore;
+		if (key == name) {
+			return {NameAction::Push, factory()};
+		}
+		else {
+			return {NameAction::Ignore, nullptr};
+		}
 	}
 
 	void
@@ -61,10 +66,11 @@ namespace Persistence {
 
 	PersistenceWrite::PersistenceWrite(const Writer & o, bool sh) : out {o}, shared {sh} { }
 
-	PersistenceStore::NameAction
-	PersistenceWrite::setName(const std::string_view key, const Selection & s)
+	PersistenceStore::NameActionSelection
+	PersistenceWrite::setName(const std::string_view key, SelectionFactory && factory)
 	{
-		if (s.needsWrite()) {
+		auto s = factory();
+		if (s->needsWrite()) {
 			if (!first) {
 				out.nextValue();
 			}
@@ -72,9 +78,9 @@ namespace Persistence {
 				first = false;
 			}
 			out.pushKey(key);
-			return NameAction::HandleAndContinue;
+			return {NameAction::HandleAndContinue, std::move(s)};
 		}
-		return NameAction::Ignore;
+		return {NameAction::Ignore, nullptr};
 	}
 
 	void
diff --git a/lib/persistence.h b/lib/persistence.h
index 1cb3af0..d38d4b1 100644
--- a/lib/persistence.h
+++ b/lib/persistence.h
@@ -149,6 +149,7 @@ namespace Persistence {
 
 	struct Persistable;
 	struct PersistenceStore {
+		using SelectionFactory = std::function<SelectionPtr()>;
 		PersistenceStore() = default;
 		virtual ~PersistenceStore() = default;
 		DEFAULT_MOVE_NO_COPY(PersistenceStore);
@@ -156,12 +157,14 @@ namespace Persistence {
 		template<typename T> [[nodiscard]] inline bool persistType(const T * const, const std::type_info & ti);
 
 		enum class NameAction { Push, HandleAndContinue, Ignore };
+		using NameActionSelection = std::pair<NameAction, SelectionPtr>;
 		template<typename Helper, typename T>
 		[[nodiscard]] inline bool
 		persistValue(const std::string_view key, T & value)
 		{
-			auto s = std::make_unique<Helper>(value);
-			const auto act {setName(key, *s)};
+			auto [act, s] = setName(key, [&value]() {
+				return std::make_unique<Helper>(value);
+			});
 			if (act != NameAction::Ignore) {
 				sel = std::move(s);
 				if (act == NameAction::HandleAndContinue) {
@@ -171,7 +174,7 @@ namespace Persistence {
 			return (act != NameAction::Push);
 		}
 
-		virtual NameAction setName(const std::string_view key, const Selection &) = 0;
+		[[nodiscard]] virtual NameActionSelection setName(const std::string_view key, SelectionFactory &&) = 0;
 		virtual void selHandler() {};
 		virtual void setType(const std::string_view, const Persistable *) = 0;
 
@@ -181,7 +184,7 @@ namespace Persistence {
 	struct PersistenceSelect : public PersistenceStore {
 		explicit PersistenceSelect(const std::string & n);
 
-		NameAction setName(const std::string_view key, const Selection &) override;
+		NameActionSelection setName(const std::string_view key, SelectionFactory &&) override;
 
 		void setType(const std::string_view, const Persistable *) override;
 
@@ -191,7 +194,7 @@ namespace Persistence {
 	struct PersistenceWrite : public PersistenceStore {
 		explicit PersistenceWrite(const Writer & o, bool sh);
 
-		NameAction setName(const std::string_view key, const Selection &) override;
+		NameActionSelection setName(const std::string_view key, SelectionFactory &&) override;
 
 		void selHandler() override;
 
-- 
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