Codechange: Add InPlaceReplacement to couple StringConsumer and Builder on the same buffer.

src/core/string_inplace.cpp

@@ -0,0 +1,63 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/**
+ * @file string_inplace.cpp Inplace-replacement of textual and binary data.
+ */
+
+#include "../stdafx.h"
+#include "string_inplace.hpp"
+#include "../safeguards.h"
+
+/**
+ * Check whether any unused bytes are left between the Builder and Consumer position.
+ */
+[[nodiscard]] bool InPlaceBuilder::AnyBytesUnused() const noexcept
+{
+	return this->consumer.GetBytesRead() > this->position;
+}
+
+/**
+ * Get number of unused bytes left between the Builder and Consumer position.
+ */
+[[nodiscard]] InPlaceBuilder::size_type InPlaceBuilder::GetBytesUnused() const noexcept
+{
+	return this->consumer.GetBytesRead() - this->position;
+}
+
+/**
+ * Append buffer.
+ */
+void InPlaceBuilder::PutBuffer(const char *str, size_type len)
+{
+	auto unused = this->GetBytesUnused();
+	if (len > unused) NOT_REACHED();
+	std::copy(str, str + len, this->dest.data() + this->position);
+	this->position += len;
+}
+
+/**
+ * Create coupled Consumer+Builder pair.
+ * @param buffer Data to consume and replace.
+ * @note The lifetime of the buffer must exceed the lifetime of both the Consumer and the Builder.
+ */
+InPlaceReplacement::InPlaceReplacement(std::span<char> buffer)
+	: consumer(buffer), builder(buffer, consumer)
+{
+}
+
+InPlaceReplacement::InPlaceReplacement(const InPlaceReplacement &src)
+	: consumer(src.consumer), builder(src.builder, consumer)
+{
+}
+
+InPlaceReplacement& InPlaceReplacement::operator=(const InPlaceReplacement &src)
+{
+	this->consumer = src.consumer;
+	this->builder.AssignBuffer(src.builder);
+	return *this;
+}