1 files changed, 96 insertions, 0 deletions
diff --git a/libyul/YulString.h b/libyul/YulString.h
new file mode 100644
index 00000000..ae01c83f
--- /dev/null
+++ b/libyul/YulString.h
@@ -0,0 +1,96 @@
+/*
+	This file is part of solidity.
+
+	solidity 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, either version 3 of the License, or
+	(at your option) any later version.
+
+	solidity 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 solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+/**
+ * String abstraction that avoids copies.
+ */
+
+#pragma once
+
+#include <boost/noncopyable.hpp>
+
+#include <map>
+#include <memory>
+#include <vector>
+#include <string>
+
+namespace dev
+{
+namespace yul
+{
+
+class YulStringRepository: boost::noncopyable
+{
+public:
+	YulStringRepository(): m_strings{std::make_shared<std::string>()}
+	{
+		m_ids[std::string{}] = 0;
+	}
+	static YulStringRepository& instance()
+	{
+		static YulStringRepository inst;
+		return inst;
+	}
+	size_t stringToId(std::string const& _string)
+	{
+		if (_string.empty())
+			return 0;
+		size_t& id = m_ids[_string];
+		if (id == 0)
+		{
+			m_strings.emplace_back(std::make_shared<std::string>(_string));
+			id = m_strings.size() - 1;
+		}
+		return id;
+	}
+	std::string const& idToString(size_t _id) const
+	{
+		return *m_strings.at(_id);
+	}
+
+private:
+	std::vector<std::shared_ptr<std::string>> m_strings;
+	std::map<std::string, size_t> m_ids;
+};
+
+class YulString
+{
+public:
+	YulString() = default;
+	explicit YulString(std::string const& _s): m_id(YulStringRepository::instance().stringToId(_s)) {}
+	YulString(YulString const&) = default;
+	YulString(YulString&&) = default;
+	YulString& operator=(YulString const&) = default;
+	YulString& operator=(YulString&&) = default;
+
+	/// This is not consistent with the string <-operator!
+	bool operator<(YulString const& _other) const { return m_id < _other.m_id; }
+	bool operator==(YulString const& _other) const { return m_id == _other.m_id; }
+	bool operator!=(YulString const& _other) const { return m_id != _other.m_id; }
+
+	bool empty() const { return m_id == 0; }
+	std::string const& str() const
+	{
+		return YulStringRepository::instance().idToString(m_id);
+	}
+
+private:
+	/// ID of the string. Assumes that the empty string has ID zero.
+	size_t m_id = 0;
+};
+
+}
+}