Introduces Result<T> for operator and implicit conversion type checks.

1 files changed, 83 insertions, 0 deletions

diff --git a/libdevcore/Result.h b/libdevcore/Result.h
new file mode 100644
index 00000000..c1abf380
--- /dev/null
+++ b/libdevcore/Result.h
@@ -0,0 +1,83 @@
+/*
+	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/>.
+*/
+#pragma once
+
+#include <string>
+
+namespace dev
+{
+
+/// Simple generic result that holds a value and an optional error message.
+/// Results can be implicitly converted to and created from the type of
+/// the value they hold.
+///
+/// Result<bool> check()
+/// {
+///		if (false)
+///			return Result<bool>(false, "Error message.")
+///		return true;
+/// }
+///
+///	A result can also be instantiated using one of the factory methods it provides:
+///
+/// using BoolResult = Result<bool>;
+/// BoolResult check()
+/// {
+///		if (false)
+///			return BoolResult::failure("Error message");
+///		return BoolResult::success(true);
+/// }
+///
+///
+struct ResultError { std::string reason; };
+
+template <class ResultType>
+class Result
+{
+public:
+	/// @{
+	/// @name Factory functions
+	/// Factory functions that provide a verbose way to create a result
+	static Result<ResultType> Ok(ResultType _value) { return Result(std::move(_value)); }
+	static Result<ResultType> Err() { return Result(ResultError{std::string()}); }
+	static Result<ResultType> Err(std::string _error) { return Result(ResultError{std::move(_error)}); }
+	/// @}
+
+	Result(ResultType _value): m_value(std::move(_value)) {}
+	Result(ResultError _error): m_error(std::move(_error.reason)) {}
+	Result(ResultType _value, ResultError _error): m_value(std::move(_value)), m_error(std::move(_error.reason)) {}
+
+	/// @{
+	/// @name Wrapper functions
+	/// Wrapper functions that provide implicit conversions to and explicit retrieval of
+	/// the value this result holds.
+	/// If the result is an error, accessing the value results in undefined behaviour.
+	operator ResultType const&() const { return m_value; }
+	ResultType& operator*() const { return m_value; }
+	ResultType const& get() const { return m_value; }
+	ResultType& get() { return m_value; }
+	/// @}
+
+	/// @returns the error message (can be empty).
+	std::string const& err() const { return m_error; }
+
+private:
+	ResultType m_value;
+	std::string m_error;
+};
+
+}