Saveload: Change SlSaveToVector to be templated, add SlSaveToTempBuffer

src/sl/company_sl.cpp

@@ -659,7 +659,7 @@ static void Save_PLYP()
 		return;
 	}
 
-	std::vector<byte> buffer = SlSaveToVector([](void *) {
+	std::vector<byte> buffer = SlSaveToVector([]() {
 		SlWriteUint32((uint32)_network_company_server_id.size());
 		MemoryDumper::GetCurrent()->CopyBytes((const uint8 *)_network_company_server_id.data(), _network_company_server_id.size());
 
@@ -681,7 +681,7 @@ static void Save_PLYP()
 		} else {
 			SlWriteByte(0);
 		}
-	}, nullptr);
+	});
 
 
 	uint8 mac[16];    /* Message authentication code */

src/sl/saveload.cpp

@@ -2052,23 +2052,25 @@ void SlAutolength(AutolengthProc *proc, void *arg)
 	_sl.dumper->CopyBytes(result.first, result.second);
 }
 
-/**
- * Run proc, saving result to a std::vector
- * @param proc The callback procedure that is called
- * @param arg The variable that will be used for the callback procedure
- */
-std::vector<byte> SlSaveToVector(AutolengthProc *proc, void *arg)
+uint8 SlSaveToTempBufferSetup()
 {
 	assert(_sl.action == SLA_SAVE);
 	NeedLength orig_need_length = _sl.need_length;
 
 	_sl.need_length = NL_NONE;
 	_sl.dumper->StartAutoLength();
-	proc(arg);
+
+	return (uint8) orig_need_length;
+}
+
+std::pair<byte *, size_t> SlSaveToTempBufferRestore(uint8 state)
+{
+	NeedLength orig_need_length = (NeedLength)state;
+
 	auto result = _sl.dumper->StopAutoLength();
 	/* Setup length */
 	_sl.need_length = orig_need_length;
-	return std::vector<uint8>(result.first, result.first + result.second);
+	return result;
 }
 
 SlLoadFromBufferState SlLoadFromBufferSetup(const byte *buffer, size_t length)

src/sl/saveload.h

@@ -712,12 +712,41 @@ void SlSetArrayIndex(uint index);
 int SlIterateArray();
 
 void SlAutolength(AutolengthProc *proc, void *arg);
-std::vector<uint8> SlSaveToVector(AutolengthProc *proc, void *arg);
 size_t SlGetFieldLength();
 void SlSetLength(size_t length);
 size_t SlCalcObjMemberLength(const void *object, const SaveLoad &sld);
 size_t SlCalcObjLength(const void *object, const SaveLoadTable &slt);
 
+/**
+ * Run proc, saving result in the autolength temp buffer
+ * @param proc The callback procedure that is called
+ * @return Span of the saved data, in the autolength temp buffer
+ */
+template <typename F>
+span<byte> SlSaveToTempBuffer(F proc)
+{
+	extern uint8 SlSaveToTempBufferSetup();
+	extern std::pair<byte *, size_t> SlSaveToTempBufferRestore(uint8 state);
+
+	uint8 state = SlSaveToTempBufferSetup();
+	proc();
+	auto result = SlSaveToTempBufferRestore(state);
+	return span<byte>(result.first, result.second);
+}
+
+/**
+ * Run proc, saving result to a std::vector
+ * This is implemented in terms of SlSaveToTempBuffer
+ * @param proc The callback procedure that is called
+ * @return a vector containing the saved data
+ */
+template <typename F>
+std::vector<uint8> SlSaveToVector(F proc)
+{
+	span<byte> result = SlSaveToTempBuffer(proc);
+	return std::vector<uint8>(result.begin(), result.end());
+}
+
 struct SlLoadFromBufferState {
 	size_t old_obj_len;
 	byte *old_bufp;