Codechange: Generalize StringBuilder.

src/core/string_builder.hpp

@@ -0,0 +1,119 @@
+/*
+ * 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_builder.hpp Compose strings from textual and binary data.
+ */
+
+#ifndef STRING_BUILDER_HPP
+#define STRING_BUILDER_HPP
+
+#include <charconv>
+
+/**
+ * Compose data into a string / buffer.
+ */
+class BaseStringBuilder {
+public:
+	using size_type = std::string_view::size_type;
+
+	virtual ~BaseStringBuilder() = default;
+
+	/**
+	 * Append buffer.
+	 */
+	virtual void PutBuffer(const char *str, size_type len) = 0;
+
+	/**
+	 * Append span.
+	 */
+	void PutBuffer(std::span<const char> str) { this->PutBuffer(str.data(), str.size()); }
+
+	/**
+	 * Append string.
+	 */
+	void Put(std::string_view str) { this->PutBuffer(str.data(), str.size()); }
+
+	void PutUint8(uint8_t value);
+	void PutSint8(int8_t value);
+	void PutUint16LE(uint16_t value);
+	void PutSint16LE(int16_t value);
+	void PutUint32LE(uint32_t value);
+	void PutSint32LE(int32_t value);
+	void PutUint64LE(uint64_t value);
+	void PutSint64LE(int64_t value);
+
+	void PutChar(char c);
+	void PutUtf8(char32_t c);
+
+	/**
+	 * Append integer 'value' in given number 'base'.
+	 */
+	template<class T>
+	void PutIntegerBase(T value, int base)
+	{
+		std::array<char, 32> buf;
+		auto result = std::to_chars(buf.data(), buf.data() + buf.size(), value, base);
+		if (result.ec != std::errc{}) return;
+		size_type len = result.ptr - buf.data();
+		this->PutBuffer(buf.data(), len);
+	}
+};
+
+/**
+ * Compose data into a growing std::string.
+ */
+class StringBuilder final : public BaseStringBuilder
+{
+	std::string *dest;
+public:
+	/**
+	 * Construct StringBuilder into destination string.
+	 * @note The lifetime of the string must exceed the lifetime of the StringBuilder.
+	 */
+	StringBuilder(std::string &dest) : dest(&dest) {}
+
+	/**
+	 * Check whether any bytes have been written.
+	 */
+	[[nodiscard]] bool AnyBytesWritten() const noexcept { return !this->dest->empty(); }
+	/**
+	 * Get number of already written bytes.
+	 */
+	[[nodiscard]] size_type GetBytesWritten() const noexcept { return this->dest->size(); }
+	/**
+	 * Get already written data.
+	 */
+	[[nodiscard]] const std::string &GetWrittenData() const noexcept { return *dest; }
+	/**
+	 * Get mutable already written data.
+	 */
+	[[nodiscard]] std::string &GetString() noexcept { return *dest; }
+
+	using BaseStringBuilder::PutBuffer;
+	void PutBuffer(const char *str, size_type len) override;
+
+	/**
+	 * Append string.
+	 */
+	StringBuilder& operator+=(std::string_view str)
+	{
+		this->Put(str);
+		return *this;
+	}
+
+	using back_insert_iterator = std::back_insert_iterator<std::string>;
+	/**
+	 * Create a back-insert-iterator.
+	 */
+	back_insert_iterator back_inserter()
+	{
+		return back_insert_iterator(*this->dest);
+	}
+};
+
+#endif /* STRING_BUILDER_HPP */