solidity/libdevcore/Result.h

/*
	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. The class is mainly designed for a result type of
/// bool or pointer type. The idea is that the default constructed value of
/// the result type is interpreted as an error value.
///
/// Result<bool> check()
/// {
///		if (false)
///			return Result<bool>::err("Error message.")
///		return true;
/// }
///

template <class ResultType>
class Result
{
public:
	/// Constructs a result with _value and an empty message.
	/// This is meant to be called with valid results. Please use
	/// the static err() member function to signal an error.
	Result(ResultType _value): Result(_value, std::string{}) {}

	/// Constructs a result with a default-constructed value and an
	/// error message.
	static Result<ResultType> err(std::string _message)
	{
		return Result{ResultType{}, std::move(_message)};
	}

	/// @{
	/// @name Wrapper functions
	/// Wrapper functions that provide implicit conversions to and explicit retrieval of
	/// the value this result holds.
	operator ResultType const&() const { return m_value; }
	ResultType const& get() const { return m_value; }
	/// @}

	/// @returns the error message (can be empty).
	std::string const& message() const { return m_message; }

	/// Merges _other into this using the _merger
	/// and appends the error messages. Meant to be called
	/// with logical operators like logical_and, etc.
	template<typename F>
	void merge(Result<ResultType> const& _other, F _merger)
	{
		m_value = _merger(m_value, _other.get());
		m_message += _other.message();
	}

private:
	explicit Result(ResultType _value, std::string _message):
		m_value(std::move(_value)),
		m_message(std::move(_message))
	{}

	ResultType m_value;
	std::string m_message;
};

}