bitcoin/src/util/overloaded.h
Russell Yanofsky d8ee8f3cd3 refactor: Make CWalletTx sync state type-safe
Current CWalletTx state representation makes it possible to set
inconsistent states that won't be handled correctly by wallet sync code
or serialized & deserialized back into the same form.

For example, it is possible to call setConflicted without setting a
conflicting block hash, or setConfirmed with no transaction index. And
it's possible update individual m_confirm and fInMempool data fields
without setting an overall consistent state that can be serialized and
handled correctly.

Fix this without changing behavior by using std::variant, instead of an
enum and collection of fields, to represent sync state, so state
tracking code is safer and more legible.

This is a first step to fixing state tracking bugs
https://github.com/bitcoin-core/bitcoin-devwiki/wiki/Wallet-Transaction-Conflict-Tracking,
by adding an extra margin of safety that can prevent new bugs from being
introduced as existing bugs are fixed.
2021-11-15 09:11:44 -05:00

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// Copyright (c) 2021 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_UTIL_OVERLOADED_H
#define BITCOIN_UTIL_OVERLOADED_H
namespace util {
//! Overloaded helper for std::visit. This helper and std::visit in general are
//! useful to write code that switches on a variant type. Unlike if/else-if and
//! switch/case statements, std::visit will trigger compile errors if there are
//! unhandled cases.
//!
//! Implementation comes from and example usage can be found at
//! https://en.cppreference.com/w/cpp/utility/variant/visit#Example
template<class... Ts> struct Overloaded : Ts... { using Ts::operator()...; };
//! Explicit deduction guide (not needed as of C++20)
template<class... Ts> Overloaded(Ts...) -> Overloaded<Ts...>;
} // namespace util
#endif // BITCOIN_UTIL_OVERLOADED_H