refactor: Replace BResult with util::Result

Rename `BResult` class to `util::Result` and update the class interface to be
more compatible with `std::optional` and with a full-featured result class
implemented in https://github.com/bitcoin/bitcoin/pull/25665. Motivation for
this change is to update existing `BResult` usages now so they don't have to
change later when more features are added in #25665.

This change makes the following improvements originally implemented in #25665:

- More explicit API. Drops potentially misleading `BResult` constructor that
  treats any bilingual string argument as an error. Adds `util::Error`
  constructor so it is never ambiguous when a result is being assigned an error
  or non-error value.

- Better type compatibility. Supports `util::Result<bilingual_str>` return
  values to hold translated messages which are not errors.

- More standard and consistent API. `util::Result` supports most of the same
  operators and methods as `std::optional`. `BResult` had a less familiar
  interface with `HasRes`/`GetObj`/`ReleaseObj` methods. The Result/Res/Obj
  naming was also not internally consistent.

- Better code organization. Puts `src/util/` code in the `util::` namespace so
  naming reflects code organization and it is obvious where the class is coming
  from. Drops "B" from name because it is undocumented what it stands for
  (bilingual?)

- Has unit tests.

src/Makefile.test.include

@@ -119,6 +119,7 @@ BITCOIN_TESTS =\
   test/random_tests.cpp \
   test/rbf_tests.cpp \
   test/rest_tests.cpp \
+  test/result_tests.cpp \
   test/reverselock_tests.cpp \
   test/rpc_tests.cpp \
   test/sanity_tests.cpp \

src/bench/wallet_loading.cpp

@@ -45,11 +45,8 @@ static void BenchUnloadWallet(std::shared_ptr<CWallet>&& wallet)
 
 static void AddTx(CWallet& wallet)
 {
-    const auto& dest = wallet.GetNewDestination(OutputType::BECH32, "");
-    assert(dest.HasRes());
-
     CMutableTransaction mtx;
-    mtx.vout.push_back({COIN, GetScriptForDestination(dest.GetObj())});
+    mtx.vout.push_back({COIN, GetScriptForDestination(*Assert(wallet.GetNewDestination(OutputType::BECH32, "")))});
     mtx.vin.push_back(CTxIn());
 
     wallet.AddToWallet(MakeTransactionRef(mtx), TxStateInactive{});

src/interfaces/wallet.h

@@ -88,7 +88,7 @@ public:
     virtual std::string getWalletName() = 0;
 
     // Get a new address.
-    virtual BResult<CTxDestination> getNewDestination(const OutputType type, const std::string label) = 0;
+    virtual util::Result<CTxDestination> getNewDestination(const OutputType type, const std::string label) = 0;
 
     //! Get public key.
     virtual bool getPubKey(const CScript& script, const CKeyID& address, CPubKey& pub_key) = 0;
@@ -139,7 +139,7 @@ public:
     virtual void listLockedCoins(std::vector<COutPoint>& outputs) = 0;
 
     //! Create transaction.
-    virtual BResult<CTransactionRef> createTransaction(const std::vector<wallet::CRecipient>& recipients,
+    virtual util::Result<CTransactionRef> createTransaction(const std::vector<wallet::CRecipient>& recipients,
         const wallet::CCoinControl& coin_control,
         bool sign,
         int& change_pos,
@@ -329,7 +329,7 @@ public:
    virtual std::string getWalletDir() = 0;
 
    //! Restore backup wallet
-   virtual BResult<std::unique_ptr<Wallet>> restoreWallet(const fs::path& backup_file, const std::string& wallet_name, std::vector<bilingual_str>& warnings) = 0;
+   virtual util::Result<std::unique_ptr<Wallet>> restoreWallet(const fs::path& backup_file, const std::string& wallet_name, std::vector<bilingual_str>& warnings) = 0;
 
    //! Return available wallets in wallet directory.
    virtual std::vector<std::string> listWalletDir() = 0;

src/qt/addresstablemodel.cpp

@@ -384,7 +384,7 @@ QString AddressTableModel::addRow(const QString &type, const QString &label, con
                 return QString();
             }
         }
-        strAddress = EncodeDestination(op_dest.GetObj());
+        strAddress = EncodeDestination(*op_dest);
     }
     else
     {

src/qt/walletcontroller.cpp

@@ -393,8 +393,8 @@ void RestoreWalletActivity::restore(const fs::path& backup_file, const std::stri
     QTimer::singleShot(0, worker(), [this, backup_file, wallet_name] {
         auto wallet{node().walletLoader().restoreWallet(backup_file, wallet_name, m_warning_message)};
 
-        m_error_message = wallet ? bilingual_str{} : wallet.GetError();
+        m_error_message = util::ErrorString(wallet);
-        if (wallet) m_wallet_model = m_wallet_controller->getOrCreateWallet(wallet.ReleaseObj());
+        if (wallet) m_wallet_model = m_wallet_controller->getOrCreateWallet(std::move(*wallet));
 
         QTimer::singleShot(0, this, &RestoreWalletActivity::finish);
     });

src/qt/walletmodel.cpp

@@ -207,7 +207,7 @@ WalletModel::SendCoinsReturn WalletModel::prepareTransaction(WalletModelTransact
 
         auto& newTx = transaction.getWtx();
         const auto& res = m_wallet->createTransaction(vecSend, coinControl, !wallet().privateKeysDisabled() /* sign */, nChangePosRet, nFeeRequired);
-        newTx = res ? res.GetObj() : nullptr;
+        newTx = res ? *res : nullptr;
         transaction.setTransactionFee(nFeeRequired);
         if (fSubtractFeeFromAmount && newTx)
             transaction.reassignAmounts(nChangePosRet);
@@ -218,7 +218,7 @@ WalletModel::SendCoinsReturn WalletModel::prepareTransaction(WalletModelTransact
             {
                 return SendCoinsReturn(AmountWithFeeExceedsBalance);
             }
-            Q_EMIT message(tr("Send Coins"), QString::fromStdString(res.GetError().translated),
+            Q_EMIT message(tr("Send Coins"), QString::fromStdString(util::ErrorString(res).translated),
                 CClientUIInterface::MSG_ERROR);
             return TransactionCreationFailed;
         }

src/test/result_tests.cpp

@@ -0,0 +1,96 @@
+// Copyright (c) 2022 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <util/result.h>
+
+#include <boost/test/unit_test.hpp>
+
+inline bool operator==(const bilingual_str& a, const bilingual_str& b)
+{
+    return a.original == b.original && a.translated == b.translated;
+}
+
+inline std::ostream& operator<<(std::ostream& os, const bilingual_str& s)
+{
+    return os << "bilingual_str('" << s.original << "' , '" << s.translated << "')";
+}
+
+BOOST_AUTO_TEST_SUITE(result_tests)
+
+struct NoCopy {
+    NoCopy(int n) : m_n{std::make_unique<int>(n)} {}
+    std::unique_ptr<int> m_n;
+};
+
+bool operator==(const NoCopy& a, const NoCopy& b)
+{
+    return *a.m_n == *b.m_n;
+}
+
+std::ostream& operator<<(std::ostream& os, const NoCopy& o)
+{
+    return os << "NoCopy(" << *o.m_n << ")";
+}
+
+util::Result<int> IntFn(int i, bool success)
+{
+    if (success) return i;
+    return util::Error{Untranslated(strprintf("int %i error.", i))};
+}
+
+util::Result<bilingual_str> StrFn(bilingual_str s, bool success)
+{
+    if (success) return s;
+    return util::Error{strprintf(Untranslated("str %s error."), s.original)};
+}
+
+util::Result<NoCopy> NoCopyFn(int i, bool success)
+{
+    if (success) return {i};
+    return util::Error{Untranslated(strprintf("nocopy %i error.", i))};
+}
+
+template <typename T>
+void ExpectResult(const util::Result<T>& result, bool success, const bilingual_str& str)
+{
+    BOOST_CHECK_EQUAL(bool(result), success);
+    BOOST_CHECK_EQUAL(util::ErrorString(result), str);
+}
+
+template <typename T, typename... Args>
+void ExpectSuccess(const util::Result<T>& result, const bilingual_str& str, Args&&... args)
+{
+    ExpectResult(result, true, str);
+    BOOST_CHECK_EQUAL(result.has_value(), true);
+    BOOST_CHECK_EQUAL(result.value(), T{std::forward<Args>(args)...});
+    BOOST_CHECK_EQUAL(&result.value(), &*result);
+}
+
+template <typename T, typename... Args>
+void ExpectFail(const util::Result<T>& result, const bilingual_str& str)
+{
+    ExpectResult(result, false, str);
+}
+
+BOOST_AUTO_TEST_CASE(check_returned)
+{
+    ExpectSuccess(IntFn(5, true), {}, 5);
+    ExpectFail(IntFn(5, false), Untranslated("int 5 error."));
+    ExpectSuccess(NoCopyFn(5, true), {}, 5);
+    ExpectFail(NoCopyFn(5, false), Untranslated("nocopy 5 error."));
+    ExpectSuccess(StrFn(Untranslated("S"), true), {}, Untranslated("S"));
+    ExpectFail(StrFn(Untranslated("S"), false), Untranslated("str S error."));
+}
+
+BOOST_AUTO_TEST_CASE(check_value_or)
+{
+    BOOST_CHECK_EQUAL(IntFn(10, true).value_or(20), 10);
+    BOOST_CHECK_EQUAL(IntFn(10, false).value_or(20), 20);
+    BOOST_CHECK_EQUAL(NoCopyFn(10, true).value_or(20), 10);
+    BOOST_CHECK_EQUAL(NoCopyFn(10, false).value_or(20), 20);
+    BOOST_CHECK_EQUAL(StrFn(Untranslated("A"), true).value_or(Untranslated("B")), Untranslated("A"));
+    BOOST_CHECK_EQUAL(StrFn(Untranslated("A"), false).value_or(Untranslated("B")), Untranslated("B"));
+}
+
+BOOST_AUTO_TEST_SUITE_END()

src/test/util/wallet.cpp

@@ -8,6 +8,7 @@
 #include <outputtype.h>
 #include <script/standard.h>
 #ifdef ENABLE_WALLET
+#include <util/check.h>
 #include <util/translation.h>
 #include <wallet/wallet.h>
 #endif
@@ -20,10 +21,7 @@ const std::string ADDRESS_BCRT1_UNSPENDABLE = "bcrt1qqqqqqqqqqqqqqqqqqqqqqqqqqqq
 std::string getnewaddress(CWallet& w)
 {
     constexpr auto output_type = OutputType::BECH32;
-    auto op_dest = w.GetNewDestination(output_type, "");
+    return EncodeDestination(*Assert(w.GetNewDestination(output_type, "")));
-    assert(op_dest.HasRes());
-
-    return EncodeDestination(op_dest.GetObj());
 }
 
 #endif // ENABLE_WALLET

src/util/result.h

@@ -5,45 +5,80 @@
 #ifndef BITCOIN_UTIL_RESULT_H
 #define BITCOIN_UTIL_RESULT_H
 
+#include <attributes.h>
 #include <util/translation.h>
 
 #include <variant>
 
-/*
+namespace util {
- * 'BResult' is a generic class useful for wrapping a return object
+
- * (in case of success) or propagating the error cause.
+struct Error {
-*/
+    bilingual_str message;
-template<class T>
+};
-class BResult {
+
+//! The util::Result class provides a standard way for functions to return
+//! either error messages or result values.
+//!
+//! It is intended for high-level functions that need to report error strings to
+//! end users. Lower-level functions that don't need this error-reporting and
+//! only need error-handling should avoid util::Result and instead use standard
+//! classes like std::optional, std::variant, and std::tuple, or custom structs
+//! and enum types to return function results.
+//!
+//! Usage examples can be found in \example ../test/result_tests.cpp, but in
+//! general code returning `util::Result<T>` values is very similar to code
+//! returning `std::optional<T>` values. Existing functions returning
+//! `std::optional<T>` can be updated to return `util::Result<T>` and return
+//! error strings usually just replacing `return std::nullopt;` with `return
+//! util::Error{error_string};`.
+template <class T>
+class Result
+{
 private:
     std::variant<bilingual_str, T> m_variant;
 
+    template <typename FT>
+    friend bilingual_str ErrorString(const Result<FT>& result);
+
 public:
-    BResult() : m_variant{Untranslated("")} {}
+    Result(T obj) : m_variant{std::in_place_index_t<1>{}, std::move(obj)} {}
-    BResult(T obj) : m_variant{std::move(obj)} {}
+    Result(Error error) : m_variant{std::in_place_index_t<0>{}, std::move(error.message)} {}
-    BResult(bilingual_str error) : m_variant{std::move(error)} {}
 
-    /* Whether the function succeeded or not */
+    //! std::optional methods, so functions returning optional<T> can change to
-    bool HasRes() const { return std::holds_alternative<T>(m_variant); }
+    //! return Result<T> with minimal changes to existing code, and vice versa.
-
+    bool has_value() const noexcept { return m_variant.index() == 1; }
-    /* In case of success, the result object */
+    const T& value() const LIFETIMEBOUND
-    const T& GetObj() const {
-        assert(HasRes());
-        return std::get<T>(m_variant);
-    }
-    T ReleaseObj()
     {
-        assert(HasRes());
+        assert(has_value());
-        return std::move(std::get<T>(m_variant));
+        return std::get<1>(m_variant);
     }
-
+    T& value() LIFETIMEBOUND
-    /* In case of failure, the error cause */
+    {
-    const bilingual_str& GetError() const {
+        assert(has_value());
-        assert(!HasRes());
+        return std::get<1>(m_variant);
-        return std::get<bilingual_str>(m_variant);
     }
-
+    template <class U>
-    explicit operator bool() const { return HasRes(); }
+    T value_or(U&& default_value) const&
+    {
+        return has_value() ? value() : std::forward<U>(default_value);
+    }
+    template <class U>
+    T value_or(U&& default_value) &&
+    {
+        return has_value() ? std::move(value()) : std::forward<U>(default_value);
+    }
+    explicit operator bool() const noexcept { return has_value(); }
+    const T* operator->() const LIFETIMEBOUND { return &value(); }
+    const T& operator*() const LIFETIMEBOUND { return value(); }
+    T* operator->() LIFETIMEBOUND { return &value(); }
+    T& operator*() LIFETIMEBOUND { return value(); }
 };
 
+template <typename T>
+bilingual_str ErrorString(const Result<T>& result)
+{
+    return result ? bilingual_str{} : std::get<0>(result.m_variant);
+}
+} // namespace util
+
 #endif // BITCOIN_UTIL_RESULT_H

src/wallet/feebumper.cpp

@@ -221,11 +221,11 @@ Result CreateRateBumpTransaction(CWallet& wallet, const uint256& txid, const CCo
     constexpr int RANDOM_CHANGE_POSITION = -1;
     auto res = CreateTransaction(wallet, recipients, RANDOM_CHANGE_POSITION, new_coin_control, false);
     if (!res) {
-        errors.push_back(Untranslated("Unable to create transaction.") + Untranslated(" ") + res.GetError());
+        errors.push_back(Untranslated("Unable to create transaction.") + Untranslated(" ") + util::ErrorString(res));
         return Result::WALLET_ERROR;
     }
 
-    const auto& txr = res.GetObj();
+    const auto& txr = *res;
     // Write back new fee if successful
     new_fee = txr.fee;
 

src/wallet/interfaces.cpp

@@ -148,7 +148,7 @@ public:
     void abortRescan() override { m_wallet->AbortRescan(); }
     bool backupWallet(const std::string& filename) override { return m_wallet->BackupWallet(filename); }
     std::string getWalletName() override { return m_wallet->GetName(); }
-    BResult<CTxDestination> getNewDestination(const OutputType type, const std::string label) override
+    util::Result<CTxDestination> getNewDestination(const OutputType type, const std::string label) override
     {
         LOCK(m_wallet->cs_wallet);
         return m_wallet->GetNewDestination(type, label);
@@ -251,17 +251,17 @@ public:
         LOCK(m_wallet->cs_wallet);
         return m_wallet->ListLockedCoins(outputs);
     }
-    BResult<CTransactionRef> createTransaction(const std::vector<CRecipient>& recipients,
+    util::Result<CTransactionRef> createTransaction(const std::vector<CRecipient>& recipients,
         const CCoinControl& coin_control,
         bool sign,
         int& change_pos,
         CAmount& fee) override
     {
         LOCK(m_wallet->cs_wallet);
-        const auto& res = CreateTransaction(*m_wallet, recipients, change_pos,
+        auto res = CreateTransaction(*m_wallet, recipients, change_pos,
                                      coin_control, sign);
-        if (!res) return res.GetError();
+        if (!res) return util::Error{util::ErrorString(res)};
-        const auto& txr = res.GetObj();
+        const auto& txr = *res;
         fee = txr.fee;
         change_pos = txr.change_pos;
 
@@ -571,12 +571,12 @@ public:
         options.require_existing = true;
         return MakeWallet(m_context, LoadWallet(m_context, name, true /* load_on_start */, options, status, error, warnings));
     }
-    BResult<std::unique_ptr<Wallet>> restoreWallet(const fs::path& backup_file, const std::string& wallet_name, std::vector<bilingual_str>& warnings) override
+    util::Result<std::unique_ptr<Wallet>> restoreWallet(const fs::path& backup_file, const std::string& wallet_name, std::vector<bilingual_str>& warnings) override
     {
         DatabaseStatus status;
         bilingual_str error;
-        BResult<std::unique_ptr<Wallet>> wallet{MakeWallet(m_context, RestoreWallet(m_context, backup_file, wallet_name, /*load_on_start=*/true, status, error, warnings))};
+        util::Result<std::unique_ptr<Wallet>> wallet{MakeWallet(m_context, RestoreWallet(m_context, backup_file, wallet_name, /*load_on_start=*/true, status, error, warnings))};
-        if (!wallet) return error;
+        if (!wallet) return util::Error{error};
         return wallet;
     }
     std::string getWalletDir() override

src/wallet/rpc/addresses.cpp

@@ -60,10 +60,10 @@ RPCHelpMan getnewaddress()
 
     auto op_dest = pwallet->GetNewDestination(output_type, label);
     if (!op_dest) {
-        throw JSONRPCError(RPC_WALLET_KEYPOOL_RAN_OUT, op_dest.GetError().original);
+        throw JSONRPCError(RPC_WALLET_KEYPOOL_RAN_OUT, util::ErrorString(op_dest).original);
     }
 
-    return EncodeDestination(op_dest.GetObj());
+    return EncodeDestination(*op_dest);
 },
     };
 }
@@ -107,9 +107,9 @@ RPCHelpMan getrawchangeaddress()
 
     auto op_dest = pwallet->GetNewChangeDestination(output_type);
     if (!op_dest) {
-        throw JSONRPCError(RPC_WALLET_KEYPOOL_RAN_OUT, op_dest.GetError().original);
+        throw JSONRPCError(RPC_WALLET_KEYPOOL_RAN_OUT, util::ErrorString(op_dest).original);
     }
-    return EncodeDestination(op_dest.GetObj());
+    return EncodeDestination(*op_dest);
 },
     };
 }

src/wallet/rpc/spend.cpp

@@ -158,14 +158,14 @@ UniValue SendMoney(CWallet& wallet, const CCoinControl &coin_control, std::vecto
     constexpr int RANDOM_CHANGE_POSITION = -1;
     auto res = CreateTransaction(wallet, recipients, RANDOM_CHANGE_POSITION, coin_control, true);
     if (!res) {
-        throw JSONRPCError(RPC_WALLET_INSUFFICIENT_FUNDS, res.GetError().original);
+        throw JSONRPCError(RPC_WALLET_INSUFFICIENT_FUNDS, util::ErrorString(res).original);
     }
-    const CTransactionRef& tx = res.GetObj().tx;
+    const CTransactionRef& tx = res->tx;
     wallet.CommitTransaction(tx, std::move(map_value), {} /* orderForm */);
     if (verbose) {
         UniValue entry(UniValue::VOBJ);
         entry.pushKV("txid", tx->GetHash().GetHex());
-        entry.pushKV("fee_reason", StringForFeeReason(res.GetObj().fee_calc.reason));
+        entry.pushKV("fee_reason", StringForFeeReason(res->fee_calc.reason));
         return entry;
     }
     return tx->GetHash().GetHex();

src/wallet/scriptpubkeyman.cpp

@@ -21,10 +21,10 @@ namespace wallet {
 //! Value for the first BIP 32 hardened derivation. Can be used as a bit mask and as a value. See BIP 32 for more details.
 const uint32_t BIP32_HARDENED_KEY_LIMIT = 0x80000000;
 
-BResult<CTxDestination> LegacyScriptPubKeyMan::GetNewDestination(const OutputType type)
+util::Result<CTxDestination> LegacyScriptPubKeyMan::GetNewDestination(const OutputType type)
 {
     if (LEGACY_OUTPUT_TYPES.count(type) == 0) {
-        return _("Error: Legacy wallets only support the \"legacy\", \"p2sh-segwit\", and \"bech32\" address types");;
+        return util::Error{_("Error: Legacy wallets only support the \"legacy\", \"p2sh-segwit\", and \"bech32\" address types")};
     }
     assert(type != OutputType::BECH32M);
 
@@ -33,7 +33,7 @@ BResult<CTxDestination> LegacyScriptPubKeyMan::GetNewDestination(const OutputTyp
     // Generate a new key that is added to wallet
     CPubKey new_key;
     if (!GetKeyFromPool(new_key, type)) {
-        return _("Error: Keypool ran out, please call keypoolrefill first");
+        return util::Error{_("Error: Keypool ran out, please call keypoolrefill first")};
     }
     LearnRelatedScripts(new_key, type);
     return GetDestinationForKey(new_key, type);
@@ -1654,11 +1654,11 @@ std::set<CKeyID> LegacyScriptPubKeyMan::GetKeys() const
     return set_address;
 }
 
-BResult<CTxDestination> DescriptorScriptPubKeyMan::GetNewDestination(const OutputType type)
+util::Result<CTxDestination> DescriptorScriptPubKeyMan::GetNewDestination(const OutputType type)
 {
     // Returns true if this descriptor supports getting new addresses. Conditions where we may be unable to fetch them (e.g. locked) are caught later
     if (!CanGetAddresses()) {
-        return _("No addresses available");
+        return util::Error{_("No addresses available")};
     }
     {
         LOCK(cs_desc_man);
@@ -1676,11 +1676,11 @@ BResult<CTxDestination> DescriptorScriptPubKeyMan::GetNewDestination(const Outpu
         std::vector<CScript> scripts_temp;
         if (m_wallet_descriptor.range_end <= m_max_cached_index && !TopUp(1)) {
             // We can't generate anymore keys
-            return _("Error: Keypool ran out, please call keypoolrefill first");
+            return util::Error{_("Error: Keypool ran out, please call keypoolrefill first")};
         }
         if (!m_wallet_descriptor.descriptor->ExpandFromCache(m_wallet_descriptor.next_index, m_wallet_descriptor.cache, scripts_temp, out_keys)) {
             // We can't generate anymore keys
-            return _("Error: Keypool ran out, please call keypoolrefill first");
+            return util::Error{_("Error: Keypool ran out, please call keypoolrefill first")};
         }
 
         CTxDestination dest;
@@ -1766,11 +1766,11 @@ bool DescriptorScriptPubKeyMan::GetReservedDestination(const OutputType type, bo
     auto op_dest = GetNewDestination(type);
     index = m_wallet_descriptor.next_index - 1;
     if (op_dest) {
-        address = op_dest.GetObj();
+        address = *op_dest;
     } else {
-        error = op_dest.GetError();
+        error = util::ErrorString(op_dest);
     }
-    return op_dest.HasRes();
+    return bool(op_dest);
 }
 
 void DescriptorScriptPubKeyMan::ReturnDestination(int64_t index, bool internal, const CTxDestination& addr)

src/wallet/scriptpubkeyman.h

@@ -172,7 +172,7 @@ protected:
 public:
     explicit ScriptPubKeyMan(WalletStorage& storage) : m_storage(storage) {}
     virtual ~ScriptPubKeyMan() {};
-    virtual BResult<CTxDestination> GetNewDestination(const OutputType type) { return Untranslated("Not supported"); }
+    virtual util::Result<CTxDestination> GetNewDestination(const OutputType type) { return util::Error{Untranslated("Not supported")}; }
     virtual isminetype IsMine(const CScript& script) const { return ISMINE_NO; }
 
     //! Check that the given decryption key is valid for this ScriptPubKeyMan, i.e. it decrypts all of the keys handled by it.
@@ -360,7 +360,7 @@ private:
 public:
     using ScriptPubKeyMan::ScriptPubKeyMan;
 
-    BResult<CTxDestination> GetNewDestination(const OutputType type) override;
+    util::Result<CTxDestination> GetNewDestination(const OutputType type) override;
     isminetype IsMine(const CScript& script) const override;
 
     bool CheckDecryptionKey(const CKeyingMaterial& master_key, bool accept_no_keys = false) override;
@@ -568,7 +568,7 @@ public:
 
     mutable RecursiveMutex cs_desc_man;
 
-    BResult<CTxDestination> GetNewDestination(const OutputType type) override;
+    util::Result<CTxDestination> GetNewDestination(const OutputType type) override;
     isminetype IsMine(const CScript& script) const override;
 
     bool CheckDecryptionKey(const CKeyingMaterial& master_key, bool accept_no_keys = false) override;

src/wallet/spend.cpp

@@ -758,7 +758,7 @@ static void DiscourageFeeSniping(CMutableTransaction& tx, FastRandomContext& rng
     }
 }
 
-static BResult<CreatedTransactionResult> CreateTransactionInternal(
+static util::Result<CreatedTransactionResult> CreateTransactionInternal(
         CWallet& wallet,
         const std::vector<CRecipient>& vecSend,
         int change_pos,
@@ -844,11 +844,11 @@ static BResult<CreatedTransactionResult> CreateTransactionInternal(
     // Do not, ever, assume that it's fine to change the fee rate if the user has explicitly
     // provided one
     if (coin_control.m_feerate && coin_selection_params.m_effective_feerate > *coin_control.m_feerate) {
-        return strprintf(_("Fee rate (%s) is lower than the minimum fee rate setting (%s)"), coin_control.m_feerate->ToString(FeeEstimateMode::SAT_VB), coin_selection_params.m_effective_feerate.ToString(FeeEstimateMode::SAT_VB));
+        return util::Error{strprintf(_("Fee rate (%s) is lower than the minimum fee rate setting (%s)"), coin_control.m_feerate->ToString(FeeEstimateMode::SAT_VB), coin_selection_params.m_effective_feerate.ToString(FeeEstimateMode::SAT_VB))};
     }
     if (feeCalc.reason == FeeReason::FALLBACK && !wallet.m_allow_fallback_fee) {
         // eventually allow a fallback fee
-        return _("Fee estimation failed. Fallbackfee is disabled. Wait a few blocks or enable -fallbackfee.");
+        return util::Error{_("Fee estimation failed. Fallbackfee is disabled. Wait a few blocks or enable -fallbackfee.")};
     }
 
     // Calculate the cost of change
@@ -874,7 +874,7 @@ static BResult<CreatedTransactionResult> CreateTransactionInternal(
         }
 
         if (IsDust(txout, wallet.chain().relayDustFee())) {
-            return _("Transaction amount too small");
+            return util::Error{_("Transaction amount too small")};
         }
         txNew.vout.push_back(txout);
     }
@@ -895,7 +895,7 @@ static BResult<CreatedTransactionResult> CreateTransactionInternal(
     // Choose coins to use
     std::optional<SelectionResult> result = SelectCoins(wallet, available_coins, /*nTargetValue=*/selection_target, coin_control, coin_selection_params);
     if (!result) {
-        return _("Insufficient funds");
+        return util::Error{_("Insufficient funds")};
     }
     TRACE5(coin_selection, selected_coins, wallet.GetName().c_str(), GetAlgorithmName(result->m_algo).c_str(), result->m_target, result->GetWaste(), result->GetSelectedValue());
 
@@ -910,7 +910,7 @@ static BResult<CreatedTransactionResult> CreateTransactionInternal(
         nChangePosInOut = rng_fast.randrange(txNew.vout.size() + 1);
     }
     else if ((unsigned int)nChangePosInOut > txNew.vout.size()) {
-        return _("Transaction change output index out of range");
+        return util::Error{_("Transaction change output index out of range")};
     }
 
     assert(nChangePosInOut != -1);
@@ -937,7 +937,7 @@ static BResult<CreatedTransactionResult> CreateTransactionInternal(
     TxSize tx_sizes = CalculateMaximumSignedTxSize(CTransaction(txNew), &wallet, &coin_control);
     int nBytes = tx_sizes.vsize;
     if (nBytes == -1) {
-        return _("Missing solving data for estimating transaction size");
+        return util::Error{_("Missing solving data for estimating transaction size")};
     }
     nFeeRet = coin_selection_params.m_effective_feerate.GetFee(nBytes);
 
@@ -997,9 +997,9 @@ static BResult<CreatedTransactionResult> CreateTransactionInternal(
                 // Error if this output is reduced to be below dust
                 if (IsDust(txout, wallet.chain().relayDustFee())) {
                     if (txout.nValue < 0) {
-                        return _("The transaction amount is too small to pay the fee");
+                        return util::Error{_("The transaction amount is too small to pay the fee")};
                     } else {
-                        return _("The transaction amount is too small to send after the fee has been deducted");
+                        return util::Error{_("The transaction amount is too small to send after the fee has been deducted")};
                     }
                 }
             }
@@ -1010,11 +1010,11 @@ static BResult<CreatedTransactionResult> CreateTransactionInternal(
 
     // Give up if change keypool ran out and change is required
     if (scriptChange.empty() && nChangePosInOut != -1) {
-        return error;
+        return util::Error{error};
     }
 
     if (sign && !wallet.SignTransaction(txNew)) {
-        return _("Signing transaction failed");
+        return util::Error{_("Signing transaction failed")};
     }
 
     // Return the constructed transaction data.
@@ -1024,17 +1024,17 @@ static BResult<CreatedTransactionResult> CreateTransactionInternal(
     if ((sign && GetTransactionWeight(*tx) > MAX_STANDARD_TX_WEIGHT) ||
         (!sign && tx_sizes.weight > MAX_STANDARD_TX_WEIGHT))
     {
-        return _("Transaction too large");
+        return util::Error{_("Transaction too large")};
     }
 
     if (nFeeRet > wallet.m_default_max_tx_fee) {
-        return TransactionErrorString(TransactionError::MAX_FEE_EXCEEDED);
+        return util::Error{TransactionErrorString(TransactionError::MAX_FEE_EXCEEDED)};
     }
 
     if (gArgs.GetBoolArg("-walletrejectlongchains", DEFAULT_WALLET_REJECT_LONG_CHAINS)) {
         // Lastly, ensure this tx will pass the mempool's chain limits
         if (!wallet.chain().checkChainLimits(tx)) {
-            return _("Transaction has too long of a mempool chain");
+            return util::Error{_("Transaction has too long of a mempool chain")};
         }
     }
 
@@ -1053,7 +1053,7 @@ static BResult<CreatedTransactionResult> CreateTransactionInternal(
     return CreatedTransactionResult(tx, nFeeRet, nChangePosInOut, feeCalc);
 }
 
-BResult<CreatedTransactionResult> CreateTransaction(
+util::Result<CreatedTransactionResult> CreateTransaction(
         CWallet& wallet,
         const std::vector<CRecipient>& vecSend,
         int change_pos,
@@ -1061,28 +1061,26 @@ BResult<CreatedTransactionResult> CreateTransaction(
         bool sign)
 {
     if (vecSend.empty()) {
-        return _("Transaction must have at least one recipient");
+        return util::Error{_("Transaction must have at least one recipient")};
     }
 
     if (std::any_of(vecSend.cbegin(), vecSend.cend(), [](const auto& recipient){ return recipient.nAmount < 0; })) {
-        return _("Transaction amounts must not be negative");
+        return util::Error{_("Transaction amounts must not be negative")};
     }
 
     LOCK(wallet.cs_wallet);
 
     auto res = CreateTransactionInternal(wallet, vecSend, change_pos, coin_control, sign);
-    TRACE4(coin_selection, normal_create_tx_internal, wallet.GetName().c_str(), res.HasRes(),
+    TRACE4(coin_selection, normal_create_tx_internal, wallet.GetName().c_str(), bool(res),
-           res ? res.GetObj().fee : 0, res ? res.GetObj().change_pos : 0);
+           res ? res->fee : 0, res ? res->change_pos : 0);
     if (!res) return res;
-    const auto& txr_ungrouped = res.GetObj();
+    const auto& txr_ungrouped = *res;
     // try with avoidpartialspends unless it's enabled already
     if (txr_ungrouped.fee > 0 /* 0 means non-functional fee rate estimation */ && wallet.m_max_aps_fee > -1 && !coin_control.m_avoid_partial_spends) {
         TRACE1(coin_selection, attempting_aps_create_tx, wallet.GetName().c_str());
         CCoinControl tmp_cc = coin_control;
         tmp_cc.m_avoid_partial_spends = true;
-        auto res_tx_grouped = CreateTransactionInternal(wallet, vecSend, change_pos, tmp_cc, sign);
+        auto txr_grouped = CreateTransactionInternal(wallet, vecSend, change_pos, tmp_cc, sign);
-        // Helper optional class for now
-        std::optional<CreatedTransactionResult> txr_grouped{res_tx_grouped.HasRes() ? std::make_optional(res_tx_grouped.GetObj()) : std::nullopt};
         // if fee of this alternative one is within the range of the max fee, we use this one
         const bool use_aps{txr_grouped.has_value() ? (txr_grouped->fee <= txr_ungrouped.fee + wallet.m_max_aps_fee) : false};
         TRACE5(coin_selection, aps_create_tx_internal, wallet.GetName().c_str(), use_aps, txr_grouped.has_value(),
@@ -1090,7 +1088,7 @@ BResult<CreatedTransactionResult> CreateTransaction(
         if (txr_grouped) {
             wallet.WalletLogPrintf("Fee non-grouped = %lld, grouped = %lld, using %s\n",
                 txr_ungrouped.fee, txr_grouped->fee, use_aps ? "grouped" : "non-grouped");
-            if (use_aps) return res_tx_grouped;
+            if (use_aps) return txr_grouped;
         }
     }
     return res;
@@ -1131,10 +1129,10 @@ bool FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& nFeeRet,
 
     auto res = CreateTransaction(wallet, vecSend, nChangePosInOut, coinControl, false);
     if (!res) {
-        error = res.GetError();
+        error = util::ErrorString(res);
         return false;
     }
-    const auto& txr = res.GetObj();
+    const auto& txr = *res;
     CTransactionRef tx_new = txr.tx;
     nFeeRet = txr.fee;
     nChangePosInOut = txr.change_pos;

src/wallet/spend.h

@@ -155,7 +155,7 @@ struct CreatedTransactionResult
  * selected by SelectCoins(); Also create the change output, when needed
  * @note passing change_pos as -1 will result in setting a random position
  */
-BResult<CreatedTransactionResult> CreateTransaction(CWallet& wallet, const std::vector<CRecipient>& vecSend, int change_pos, const CCoinControl& coin_control, bool sign = true);
+util::Result<CreatedTransactionResult> CreateTransaction(CWallet& wallet, const std::vector<CRecipient>& vecSend, int change_pos, const CCoinControl& coin_control, bool sign = true);
 
 /**
  * Insert additional inputs into the transaction by

src/wallet/test/availablecoins_tests.cpp

@@ -33,7 +33,7 @@ public:
             constexpr int RANDOM_CHANGE_POSITION = -1;
             auto res = CreateTransaction(*wallet, {recipient}, RANDOM_CHANGE_POSITION, dummy);
             BOOST_CHECK(res);
-            tx = res.GetObj().tx;
+            tx = res->tx;
         }
         wallet->CommitTransaction(tx, {}, {});
         CMutableTransaction blocktx;
@@ -57,7 +57,7 @@ public:
 BOOST_FIXTURE_TEST_CASE(BasicOutputTypesTest, AvailableCoinsTestingSetup)
 {
     CoinsResult available_coins;
-    BResult<CTxDestination> dest;
+    util::Result<CTxDestination> dest{util::Error{}};
     LOCK(wallet->cs_wallet);
 
     // Verify our wallet has one usable coinbase UTXO before starting
@@ -75,28 +75,28 @@ BOOST_FIXTURE_TEST_CASE(BasicOutputTypesTest, AvailableCoinsTestingSetup)
 
     // Bech32m
     dest = wallet->GetNewDestination(OutputType::BECH32M, "");
-    BOOST_ASSERT(dest.HasRes());
+    BOOST_ASSERT(dest);
-    AddTx(CRecipient{{GetScriptForDestination(dest.GetObj())}, 1 * COIN, /*fSubtractFeeFromAmount=*/true});
+    AddTx(CRecipient{{GetScriptForDestination(*dest)}, 1 * COIN, /*fSubtractFeeFromAmount=*/true});
     available_coins = AvailableCoins(*wallet);
     BOOST_CHECK_EQUAL(available_coins.bech32m.size(), 2U);
 
     // Bech32
     dest = wallet->GetNewDestination(OutputType::BECH32, "");
-    BOOST_ASSERT(dest.HasRes());
+    BOOST_ASSERT(dest);
-    AddTx(CRecipient{{GetScriptForDestination(dest.GetObj())}, 2 * COIN, /*fSubtractFeeFromAmount=*/true});
+    AddTx(CRecipient{{GetScriptForDestination(*dest)}, 2 * COIN, /*fSubtractFeeFromAmount=*/true});
     available_coins = AvailableCoins(*wallet);
     BOOST_CHECK_EQUAL(available_coins.bech32.size(), 2U);
 
     // P2SH-SEGWIT
     dest = wallet->GetNewDestination(OutputType::P2SH_SEGWIT, "");
-    AddTx(CRecipient{{GetScriptForDestination(dest.GetObj())}, 3 * COIN, /*fSubtractFeeFromAmount=*/true});
+    AddTx(CRecipient{{GetScriptForDestination(*dest)}, 3 * COIN, /*fSubtractFeeFromAmount=*/true});
     available_coins = AvailableCoins(*wallet);
     BOOST_CHECK_EQUAL(available_coins.P2SH_segwit.size(), 2U);
 
     // Legacy (P2PKH)
     dest = wallet->GetNewDestination(OutputType::LEGACY, "");
-    BOOST_ASSERT(dest.HasRes());
+    BOOST_ASSERT(dest);
-    AddTx(CRecipient{{GetScriptForDestination(dest.GetObj())}, 4 * COIN, /*fSubtractFeeFromAmount=*/true});
+    AddTx(CRecipient{{GetScriptForDestination(*dest)}, 4 * COIN, /*fSubtractFeeFromAmount=*/true});
     available_coins = AvailableCoins(*wallet);
     BOOST_CHECK_EQUAL(available_coins.legacy.size(), 2U);
 }

src/wallet/test/coinselector_tests.cpp

@@ -74,9 +74,7 @@ static void add_coin(CoinsResult& available_coins, CWallet& wallet, const CAmoun
     tx.vout.resize(nInput + 1);
     tx.vout[nInput].nValue = nValue;
     if (spendable) {
-        auto op_dest = wallet.GetNewDestination(OutputType::BECH32, "");
+        tx.vout[nInput].scriptPubKey = GetScriptForDestination(*Assert(wallet.GetNewDestination(OutputType::BECH32, "")));
-        assert(op_dest.HasRes());
-        tx.vout[nInput].scriptPubKey = GetScriptForDestination(op_dest.GetObj());
     }
     uint256 txid = tx.GetHash();
 

src/wallet/test/fuzz/notifications.cpp

@@ -69,14 +69,13 @@ struct FuzzedWallet {
     CScript GetScriptPubKey(FuzzedDataProvider& fuzzed_data_provider)
     {
         auto type{fuzzed_data_provider.PickValueInArray(OUTPUT_TYPES)};
-        BResult<CTxDestination> op_dest;
+        util::Result<CTxDestination> op_dest{util::Error{}};
         if (fuzzed_data_provider.ConsumeBool()) {
             op_dest = wallet->GetNewDestination(type, "");
         } else {
             op_dest = wallet->GetNewChangeDestination(type);
         }
-        assert(op_dest.HasRes());
+        return GetScriptForDestination(*Assert(op_dest));
-        return GetScriptForDestination(op_dest.GetObj());
     }
 };
 

src/wallet/test/spend_tests.cpp

@@ -35,7 +35,7 @@ BOOST_FIXTURE_TEST_CASE(SubtractFee, TestChain100Setup)
         coin_control.m_change_type = OutputType::LEGACY;
         auto res = CreateTransaction(*wallet, {recipient}, RANDOM_CHANGE_POSITION, coin_control);
         BOOST_CHECK(res);
-        const auto& txr = res.GetObj();
+        const auto& txr = *res;
         BOOST_CHECK_EQUAL(txr.tx->vout.size(), 1);
         BOOST_CHECK_EQUAL(txr.tx->vout[0].nValue, recipient.nAmount + leftover_input_amount - txr.fee);
         BOOST_CHECK_GT(txr.fee, 0);

src/wallet/test/wallet_tests.cpp

@@ -536,7 +536,7 @@ public:
             constexpr int RANDOM_CHANGE_POSITION = -1;
             auto res = CreateTransaction(*wallet, {recipient}, RANDOM_CHANGE_POSITION, dummy);
             BOOST_CHECK(res);
-            tx = res.GetObj().tx;
+            tx = res->tx;
         }
         wallet->CommitTransaction(tx, {}, {});
         CMutableTransaction blocktx;
@@ -918,8 +918,8 @@ BOOST_FIXTURE_TEST_CASE(wallet_sync_tx_invalid_state_test, TestingSetup)
 
     // Add tx to wallet
     const auto& op_dest = wallet.GetNewDestination(OutputType::BECH32M, "");
-    BOOST_ASSERT(op_dest.HasRes());
+    BOOST_ASSERT(op_dest);
-    const CTxDestination& dest = op_dest.GetObj();
+    const CTxDestination& dest = *op_dest;
 
     CMutableTransaction mtx;
     mtx.vout.push_back({COIN, GetScriptForDestination(dest)});

src/wallet/wallet.cpp

@@ -2330,24 +2330,24 @@ bool CWallet::TopUpKeyPool(unsigned int kpSize)
     return res;
 }
 
-BResult<CTxDestination> CWallet::GetNewDestination(const OutputType type, const std::string label)
+util::Result<CTxDestination> CWallet::GetNewDestination(const OutputType type, const std::string label)
 {
     LOCK(cs_wallet);
     auto spk_man = GetScriptPubKeyMan(type, false /* internal */);
     if (!spk_man) {
-        return strprintf(_("Error: No %s addresses available."), FormatOutputType(type));
+        return util::Error{strprintf(_("Error: No %s addresses available."), FormatOutputType(type))};
     }
 
     spk_man->TopUp();
     auto op_dest = spk_man->GetNewDestination(type);
     if (op_dest) {
-        SetAddressBook(op_dest.GetObj(), label, "receive");
+        SetAddressBook(*op_dest, label, "receive");
     }
 
     return op_dest;
 }
 
-BResult<CTxDestination> CWallet::GetNewChangeDestination(const OutputType type)
+util::Result<CTxDestination> CWallet::GetNewChangeDestination(const OutputType type)
 {
     LOCK(cs_wallet);
 
@@ -2355,7 +2355,7 @@ BResult<CTxDestination> CWallet::GetNewChangeDestination(const OutputType type)
     bilingual_str error;
     ReserveDestination reservedest(this, type);
     if (!reservedest.GetReservedDestination(dest, true, error)) {
-        return error;
+        return util::Error{error};
     }
 
     reservedest.KeepDestination();

src/wallet/wallet.h

@@ -670,8 +670,8 @@ public:
      */
     void MarkDestinationsDirty(const std::set<CTxDestination>& destinations) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
 
-    BResult<CTxDestination> GetNewDestination(const OutputType type, const std::string label);
+    util::Result<CTxDestination> GetNewDestination(const OutputType type, const std::string label);
-    BResult<CTxDestination> GetNewChangeDestination(const OutputType type);
+    util::Result<CTxDestination> GetNewChangeDestination(const OutputType type);
 
     isminetype IsMine(const CTxDestination& dest) const EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
     isminetype IsMine(const CScript& script) const EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);