From 44ee58911b3ffbe9e48e5278bdc73edaf618facd Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Sun, 9 May 2021 20:08:31 +0100
Subject: Don't write null value for pointers

Null is a sensible default which can't be defaulted to anything else sane
---
 lib/persistence.cpp | 29 +++++++++++++++++++----------
 lib/persistence.h   | 18 +++++++++++++-----
 2 files changed, 32 insertions(+), 15 deletions(-)

diff --git a/lib/persistence.cpp b/lib/persistence.cpp
index b85bff2..405c7ec 100644
--- a/lib/persistence.cpp
+++ b/lib/persistence.cpp
@@ -38,7 +38,7 @@ namespace Persistence {
 	PersistenceSelect::PersistenceSelect(const std::string & n) : name {n} { }
 
 	PersistenceStore::NameAction
-	PersistenceSelect::setName(const std::string_view key)
+	PersistenceSelect::setName(const std::string_view key, const Selection &)
 	{
 		return (key == name) ? NameAction::Push : NameAction::Ignore;
 	}
@@ -51,16 +51,19 @@ namespace Persistence {
 	PersistenceWrite::PersistenceWrite(const Writer & o, bool sh) : out {o}, shared {sh} { }
 
 	PersistenceStore::NameAction
-	PersistenceWrite::setName(const std::string_view key)
-	{
-		if (!first) {
-			out.nextValue();
-		}
-		else {
-			first = false;
+	PersistenceWrite::setName(const std::string_view key, const Selection & s)
+	{
+		if (s.needsWrite()) {
+			if (!first) {
+				out.nextValue();
+			}
+			else {
+				first = false;
+			}
+			out.pushKey(key);
+			return NameAction::HandleAndContinue;
 		}
-		out.pushKey(key);
-		return NameAction::HandleAndContinue;
+		return NameAction::Ignore;
 	}
 
 	void
@@ -135,6 +138,12 @@ namespace Persistence {
 	{
 	}
 
+	bool
+	Selection::needsWrite() const
+	{
+		return true;
+	}
+
 	void
 	Selection::write(const Writer &) const
 	{
diff --git a/lib/persistence.h b/lib/persistence.h
index 0eba1ab..252afde 100644
--- a/lib/persistence.h
+++ b/lib/persistence.h
@@ -53,6 +53,7 @@ namespace Persistence {
 		virtual void beforeValue(Stack &);
 		[[nodiscard]] virtual SelectionPtr select(const std::string &);
 
+		[[nodiscard]] virtual bool needsWrite() const;
 		virtual void write(const Writer &) const;
 	};
 
@@ -108,9 +109,10 @@ namespace Persistence {
 		[[nodiscard]] inline bool
 		persistValue(const std::string_view key, T & value)
 		{
-			const auto act {setName(key)};
+			SelectionT<T> s {value};
+			const auto act {setName(key, s)};
 			if (act != NameAction::Ignore) {
-				sel = SelectionV<T>::make(value);
+				sel = std::make_unique<decltype(s)>(std::move(s));
 				if (act == NameAction::HandleAndContinue) {
 					selHandler();
 				}
@@ -118,7 +120,7 @@ namespace Persistence {
 			return (act != NameAction::Push);
 		}
 
-		virtual NameAction setName(const std::string_view key) = 0;
+		virtual NameAction setName(const std::string_view key, const Selection &) = 0;
 		virtual void selHandler() {};
 		virtual void setType(const std::string_view, const Persistable *) = 0;
 
@@ -128,7 +130,7 @@ namespace Persistence {
 	struct PersistenceSelect : public PersistenceStore {
 		explicit PersistenceSelect(const std::string & n);
 
-		NameAction setName(const std::string_view key) override;
+		NameAction setName(const std::string_view key, const Selection &) override;
 
 		void setType(const std::string_view, const Persistable *) override;
 
@@ -138,7 +140,7 @@ namespace Persistence {
 	struct PersistenceWrite : public PersistenceStore {
 		explicit PersistenceWrite(const Writer & o, bool sh);
 
-		NameAction setName(const std::string_view key) override;
+		NameAction setName(const std::string_view key, const Selection &) override;
 
 		void selHandler() override;
 
@@ -399,6 +401,12 @@ namespace Persistence {
 			stk.pop();
 		}
 
+		[[nodiscard]] bool
+		needsWrite() const override
+		{
+			return this->v != nullptr;
+		}
+
 		void
 		write(const Writer & out) const override
 		{
-- 
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