dd065dae9fcebd6806ff67703ffa8128e80b97cc refactor: Make mapBlocksUnknownParent local, and rename it (Hennadii Stepanov)
Pull request description:
This PR is a second attempt at #19594. This PR has two motivations:
- Improve code hygiene by eliminating a global variable, `mapBlocksUnknownParent`
- Fix fuzz test OOM when running too long ([see #19594 comment](https://github.com/bitcoin/bitcoin/pull/19594#issuecomment-958801638))
A minor added advantage is to release `mapBlocksUnknownParent` memory when the reindexing phase is done. The current situation is somewhat similar to a memory leak because this map exists unused for the remaining lifetime of the process. It's true that this map should be empty of data elements after use, but its internal metadata (indexing structures, etc.) can have non-trivial size because there can be many thousands of simultaneous elements in this map.
This PR helps our efforts to reduce the use of global variables. This variable isn't just global, it's hidden inside a function (it looks like a local variable but has the `static` attribute).
This global variable exists because the `-reindex` processing code calls `LoadExternalBlockFile()` multiple times (once for each block file), but that function must preserve some state between calls (the `mapBlocksUnknownParent` map). This PR fixes this by allocating this map as a local variable in the caller's scope and passing it in on each call. When reindexing completes, the map goes out of scope and is deallocated.
I tested this manually by reindexing on mainnet and signet. Also, the existing `feature_reindex.py` functional test passes.
ACKs for top commit:
mzumsande:
re-ACK dd065dae9fcebd6806ff67703ffa8128e80b97cc
theStack:
re-ACK dd065dae9fcebd6806ff67703ffa8128e80b97cc
shaavan:
reACK dd065dae9fcebd6806ff67703ffa8128e80b97cc
Tree-SHA512: 9cd20e44d2fa1096dd405bc107bc065ea8f904f5b3f63080341b08d8cf57b790df565f58815c2f331377d044d5306708b4bf6bdfc5ef8d0ed85d8e97d744732c
b4b657ba57a2ce31b3c21ea9245aad26d5b06a57 refactor: log `nEvicted` message in `LimitOrphans` then return void (chinggg)
Pull request description:
Fix https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=49347
LimitOrphans() can log expired tx and it should log evicted tx as well instead of returning the `nEvicted` number for caller to print the message.
Since `LimitOrphans()` now returns void, the redundant assertion check in fuzz test is also removed.
Top commit has no ACKs.
Tree-SHA512: 18c41702321b0e59812590cd389f3163831d431f4ebdc3b3e1e0698496a6bdbac52288f28f779237a58813c6717da1a35e8933d509822978ff726c1b13cfc778
71d1d13627ccd27319f347e2d8167c8fe8a433f4 test: add unit test for AvailableCoins (josibake)
da03cb41a4ce15ebceee7fa4a4fdd2d3602fe284 test: functional test for new coin selection logic (josibake)
438e04845bf3302b7f459a50e88a1b772527f1e6 wallet: run coin selection by `OutputType` (josibake)
77b07072061c59f50c69be29fbcddf0d433e1077 refactor: use CoinsResult struct in SelectCoins (josibake)
2e67291ca3ab2d8f498fa910738ca655fde11c5e refactor: store by OutputType in CoinsResult (josibake)
Pull request description:
# Concept
Following https://github.com/bitcoin/bitcoin/pull/23789, Bitcoin Core wallet will now generate a change address that matches the payment address type. This improves privacy by not revealing which of the outputs is the change at the time of the transaction in scenarios where the input address types differ from the payment address type. However, information about the change can be leaked in a later transaction. This proposal attempts to address that concern.
## Leaking information in a later transaction
Consider the following scenario:
1. Alice has a wallet with bech32 type UTXOs and pays Bob, who gives her a P2SH address
2. Alice's wallet generates a P2SH change output, preserving her privacy in `txid: a`
3. Alice then pays Carol, who gives her a bech32 address
4. Alice's wallet combines the P2SH UTXO with a bech32 UTXO and `txid: b` has two bech32 outputs
From a chain analysis perspective, it is reasonable to infer that the P2SH input in `txid: b` was the change from `txid: a`. To avoid leaking information in this scenario, Alice's wallet should avoid picking the P2SH output and instead fund the transaction with only bech32 Outputs. If the payment to Carol can be funded with just the P2SH output, it should be preferred over the bech32 outputs as this will convert the P2SH UTXO to bech32 UTXOs via the payment and change outputs of the new transaction.
**TLDR;** Avoid mixing output types, spend non-default `OutputTypes` when it is economical to do so.
# Approach
`AvailableCoins` now populates a struct, which makes it easier to access coins by `OutputType`. Coin selection tries to find a funding solution by each output type and chooses the most economical by waste metric. If a solution can't be found without mixing, coin selection runs over the entire wallet, allowing mixing, which is the same as the current behavior.
I've also added a functional test (`test/functional/wallet_avoid_mixing_output_types.py`) and unit test (`src/wallet/test/availablecoins_tests.cpp`.
ACKs for top commit:
achow101:
re-ACK 71d1d13627ccd27319f347e2d8167c8fe8a433f4
aureleoules:
ACK 71d1d13627ccd27319f347e2d8167c8fe8a433f4.
Xekyo:
reACK 71d1d13627ccd27319f347e2d8167c8fe8a433f4 via `git range-diff master 6530d19 71d1d13`
LarryRuane:
ACK 71d1d13627ccd27319f347e2d8167c8fe8a433f4
Tree-SHA512: 2e0716efdae5adf5479446fabc731ae81d595131d3b8bade98b64ba323d0e0c6d964a67f8c14c89c428998bda47993fa924f3cfca1529e2bd49eaa4e31b7e426
4e616d20c9e92b5118a07d4a4b8562fffc66e767 test: check that combining PSBTs with different txs fails (Sebastian Falbesoner)
2a428c79897761579efc990aaf810b0eb3e572b6 test: support passing PSBTMaps directly to PSBT ctor (Sebastian Falbesoner)
Pull request description:
This PR adds missing test coverage for the `combinepsbt` RPC, in the case of combining two PSBTs with different transactions:
b8067cd435/src/psbt.cpp (L24-L27)
The calling function `CombinePSBTs` checks for the false return value and then returns the transaction error string `PSBT_MISMATCH`:
b8067cd435/src/psbt.cpp (L433-L435)b8067cd435/src/util/error.cpp (L30-L31)
ACKs for top commit:
instagibbs:
reACK 4e616d20c9
achow101:
ACK 4e616d20c9e92b5118a07d4a4b8562fffc66e767
Tree-SHA512: 45b2b224b13b44ad69ae62e4bc20f74cab32770cf8127b026ec47a7520f7253148fdbf1fad612afece59e45a6738bef9a351ae87ea98dc83d095cc78f6db0318
c320cddb1b57a9c9911054fc440f7a12aaea61b5 [unit tests] individual RBF Rules in isolation (glozow)
Pull request description:
Test each RBF rule more thoroughly and in isolation so we're not relying on things like overall mempool acceptance logic, ordering of mempool checks, RPC results, etc.
RBF was pretty recently refactored out, so there isn't much unit test coverage. From https://marcofalke.github.io/btc_cov/test_bitcoin.coverage/src/policy/rbf.cpp.gcov.html:
ACKs for top commit:
instagibbs:
reACK c320cddb1b
jonatack:
ACK c320cddb1b57a9c9911054fc440f7a12aaea61b5
w0xlt:
ACK c320cddb1b
Tree-SHA512: dab555214496255801b9ea92b7bf708bba1ff23edf055c85e29be5eab7d7a863440ee19588aacdce54b2c03feaa4b5963eb159ed89473560bd228737cbfec160
Test each component of the RBF policy in isolation. Unlike the RBF
functional tests, these do not rely on things like RPC results, mempool
submission, etc.
ba9a8e6cc1d1e9746f74e8c75af5c6c0a49f25c3 test: Drop unused boost workaround (Hennadii Stepanov)
Pull request description:
This PR is a follow up of bitcoin/bitcoin#24065 and removes the workaround which has already been removed in other [places](https://github.com/bitcoin/bitcoin/pull/24065/files#diff-19427b0dd1a791adc728c82e88f267751ba4f1c751e19262cac03cccd2822216).
Moreover, this workaround won't be required even if bitcoin/bitcoin#25696 is ever merged.
ACKs for top commit:
fanquake:
ACK ba9a8e6cc1d1e9746f74e8c75af5c6c0a49f25c3
Tree-SHA512: db19fc1550252d7a82a08f388ff6078c78452365e74b41e7bc36cbbc4d0fed9342636e8f2371bb8e78c9d11ee721d6363bcc21d11787f3aac967a6c4a9cc346f
`LimitOrphans()` can log expired tx and it should log evicted tx as well
instead of returning the number for caller to print the message.
Since `LimitOrphans()` now return void, the redundant assertion check in
fuzz test is also removed.
e838a9847580527b8321d65e57b1c53cc2af6bf4 depends: re-enable using -flto when building expat (fanquake)
304452558c7f6f5e32ba13d8f05325790c8a4f5f depends: expat 2.4.8 (fanquake)
Pull request description:
Currently, when building the expat package in depends, using `-flto` (`LTO=1`), the configure check can fail, because it cannot determine the system endianess:
```bash
configure:18718: result: unknown
configure:18733: error: unknown endianness
presetting ac_cv_c_bigendian=no (or yes) will help
```
Fix that by defining `_DEFAULT_SOURCE`, which in turn defines `__USE_MISC` (`features.h`):
```c
#if defined _DEFAULT_SOURCE
# define __USE_MISC1
#endif
```
which exposes additional definitions in `endian.h`:
```c
#include <features.h>
/* Get the definitions of __*_ENDIAN, __BYTE_ORDER, and __FLOAT_WORD_ORDER. */
#include <bits/endian.h>
#ifdef __USE_MISC
# define LITTLE_ENDIAN__LITTLE_ENDIAN
# define BIG_ENDIAN__BIG_ENDIAN
# define PDP_ENDIAN__PDP_ENDIAN
# define BYTE_ORDER__BYTE_ORDER
#endif
```
and gives us a working configure.
You could test building this change with Guix + LTO with [this branch](https://github.com/fanquake/bitcoin/tree/lto_in_guix). Note that that build may fail for other reasons (on x86_64), unrelated to this change.
Some related upstream discussion:
https://bugs.gentoo.org/757681https://forums.gentoo.org/viewtopic-t-1013786.html
ACKs for top commit:
hebasto:
re-ACK e838a9847580527b8321d65e57b1c53cc2af6bf4, only [suggested](https://github.com/bitcoin/bitcoin/pull/25697#discussion_r929735675) changes since my recent [review](https://github.com/bitcoin/bitcoin/pull/25697#pullrequestreview-1050657421).
jarolrod:
code review ACK e838a9847580527b8321d65e57b1c53cc2af6bf4
Tree-SHA512: 9dbf64c9bd1fd995a4d1addc011ffeff83d50df736030012346c97605e63aed4b5bac390a81abe646c1be28ad6fd600f64560dcb26bbc2edf5d513ca3b180bfa
fa74e726c414f5f7a1e63126a69463491f66e0ec refactor: Make FEELER_SLEEP_WINDOW type safe (std::chrono) (MacroFake)
fa3b3cb9b5d944d34b1d5ac3e102ac333482a475 Expose underlying clock in CThreadInterrupt (MacroFake)
Pull request description:
This gets rid of the `value*1000` manual conversion.
ACKs for top commit:
naumenkogs:
utACK fa74e726c414f5f7a1e63126a69463491f66e0ec
dergoegge:
Code review ACK fa74e726c414f5f7a1e63126a69463491f66e0ec
Tree-SHA512: 90409c05c25f0dd2f1c4dead78f707ebfd78b7d84ea4db9fcefd9c4958a1a3338ac657cd9e99eb8b47d52d4485fa3c947dce4ee1559fb56ae65878685e1ed9a3
fa2247a9f9754d90ea60f254f6c0ed881c55772b refactor: Make CTransaction constructor explicit (MacroFake)
Pull request description:
It involves calculating two hashes, so the performance impact should be
made explicit.
Also, add the module to iwyu.
ACKs for top commit:
aureleoules:
ACK fa2247a9f9754d90ea60f254f6c0ed881c55772b.
hebasto:
ACK fa2247a9f9754d90ea60f254f6c0ed881c55772b, I have reviewed the code and it looks OK, I agree it can be merged.
Tree-SHA512: e236c352a472c7edfd4f0319a5a16a59f627b0ab7eb8531b53c75d730a3fa3e990a939978dcd952cd73e647925fc79bfa6d9fd87624bbc3ef180f40f95acef19
fa57c449cf45a4f1df195970c711bba8f02f3cc6 fuzz: Remove no-op SetMempoolConstraints (MacroFake)
Pull request description:
Now that the mempool no longer uses the args manager (after commit e4e201dfd9a9dbd8e22cac688dbbde16234cd937), there is no point setting the mempool limits after it is constructed.
Fix that by setting them once right before the mempool is constructed.
ACKs for top commit:
dongcarl:
utACK fa57c449cf45a4f1df195970c711bba8f02f3cc6
glozow:
utACK fa57c449cf45a4f1df195970c711bba8f02f3cc6
Tree-SHA512: d236f9cdcee8c2076272b82c97f8a5942f1ecf119ab36edafd42088ef97554592348a61e1fbe504fd52b30301ef0177813042599ad12e8cb95b4a20586c85bb0
fa28d0f3c3fe528dae7fd6dc7725219b9bdf0e1b scripted-diff: Replace NullUniValue with UniValue::VNULL (MacroFake)
fa962103e8eb0b078b83943a21831be39e7716c9 fuzz: refactor: Replace NullUniValue with UniValue{} (MacroFake)
Pull request description:
This refactor is needed to disable the (potentially expensive for large json) UniValue copy constructors.
ACKs for top commit:
fanquake:
ACK fa28d0f3c3fe528dae7fd6dc7725219b9bdf0e1b
Tree-SHA512: 7d4204cce0a6fc4ecda96973de77d15b7e4c7caa3e0e890e1f5b9a4b9ace8b240b1f7565d6ab586e168a5fa1201b6c60a924868ef34d6abfbfd8ab7f0f99fbc7
850b0850ccacc4e4f7e82ce2291a111132eae756 fix comment spellings from the codespell lint (Greg Weber)
Pull request description:
test/lint/all-lint.py includes the codespell lint
ACKs for top commit:
aureleoules:
ACK 850b0850ccacc4e4f7e82ce2291a111132eae756.
Tree-SHA512: bf63690da2652886e705d6594903bab67ff0f35a0e5a5505f063827f5148ebce47681e541cbe0e52396baf1addb25d9fe50e5faa9176456f579a7cd2f1321c44
If we don't set this explicitly, then qt will still use it's default
windows ar, when building with LTO (when we want it to use gcc-ar).
So set `QMAKE_LIB` which is used for win32, and defaults to `ar -rc`.
This way we always get the correct ar.
Issue can be seen building in Guix with LTO. i.e:
```bash
x86_64-w64-mingw32-ar: .obj/release/hb-blob.o: plugin needed to handle lto object
```
4fa79837ad19fada3a3df3fb490617f6ca4606e0 psbt: Fix unsigned integer overflow (Aurèle Oulès)
Pull request description:
Fixes#25692.
This change prevents an unsigned integer overflow during the deserialization of a PSBT.
ACKs for top commit:
achow101:
ACK 4fa79837ad19fada3a3df3fb490617f6ca4606e0
Tree-SHA512: 0863d4d31ada1ba50632b6a66cb4c694c0a15680a90cf9370129cf3db15e3c10e65610b779db047d5a4cc7c920708b728948708e4023e916099c6bfe730f01f9
This is required for removing the UniValue copy constructor.
-BEGIN VERIFY SCRIPT-
sed -i 's/return NullUniValue/return UniValue::VNULL/g' $(git grep -l NullUniValue ':(exclude)src/univalue')
-END VERIFY SCRIPT-
3a61fc56a0ad6ed58570350dcfd9ed2d10239b48 refactor: move CBlockIndex#ToString() from header to implementation (Jon Atack)
57865eb51288852c3ce99607eff76c61ae5f5365 CDiskBlockIndex: rename GetBlockHash() to ConstructBlockHash() (Jon Atack)
99e8ec8721a52cd08bdca31f6e926c9c1ce281fb CDiskBlockIndex: remove unused ToString() class member (Jon Atack)
14aeece462b149eaf0d28a37d55cc169df99b2cb CBlockIndex: ensure phashBlock is not nullptr before dereferencing (Jon Atack)
Pull request description:
Fix a few design issues, potential footguns and inconsistent behavior in the CBlockIndex and CDiskBlockIndex classes.
- Ensure phashBlock in `CBlockIndex#GetBlockHash()` is not nullptr before dereferencing and remove a now-redundant assert preceding a GetBlockHash() caller. This protects against UB here, and in case of failure (which would indicate a consensus bug), the debug log will print `bitcoind: chain.h:265: uint256 CBlockIndex::GetBlockHash() const: Assertion 'phashBlock != nullptr' failed. Aborted` instead of `Segmentation fault`.
- Remove the unused `CDiskBlockIndex#ToString()` class member, and mark the inherited `CBlockIndex#ToString()` public interface member as deleted to disallow calling it in the derived CDiskBlockIndex class.
- Rename the `CDiskBlockIndex GetBlockHash()` class member to `ConstructBlockHash()`, which also makes sense as they perform different operations to return a blockhash, and mark the inherited `CBlockIndex#GetBlockHash()` public interface member as deleted to disallow calling it in the derived CDiskBlockIndex class.
- Move `CBlockIndex#ToString()` from header to implementation, which also allows dropping `tinyformat.h` from the header file.
Rationale and discussion regarding the CDiskBlockIndex changes:
Here is a failing test on master that demonstrates the inconsistent behavior of the current design: calling the same inherited public interface functions on the same CDiskBlockIndex object should yield identical behavior, but does not.
```diff
diff --git a/src/test/validation_chainstatemanager_tests.cpp b/src/test/validation_chainstatemanager_tests.cpp
index 6dc522b421..dac3840f32 100644
--- a/src/test/validation_chainstatemanager_tests.cpp
+++ b/src/test/validation_chainstatemanager_tests.cpp
@@ -240,6 +240,15 @@ BOOST_FIXTURE_TEST_CASE(chainstatemanager_activate_snapshot, TestChain100Setup)
const CBlockIndex* tip = chainman.ActiveTip();
BOOST_CHECK_EQUAL(tip->nChainTx, au_data.nChainTx);
+ // CDiskBlockIndex "is a" CBlockIndex, as it publicly inherits from it.
+ // Test that calling the same inherited interface functions on the same
+ // object yields identical behavior.
+ CDiskBlockIndex index{tip};
+ CBlockIndex *pB = &index;
+ CDiskBlockIndex *pD = &index;
+ BOOST_CHECK_EQUAL(pB->GetBlockHash(), pD->GetBlockHash());
+ BOOST_CHECK_EQUAL(pB->ToString(), pD->ToString());
```
(build and run: `$ ./src/test/test_bitcoin -t validation_chainstatemanager_tests`)
The GetBlockHash() test assertion only passes on master because the different methods invoked by the current design happen to return the same result. If one of the two is changed, it fails like the ToString() assertion does.
Redefining inherited non-virtual functions is well-documented as incorrect design to avoid inconsistent behavior (see Scott Meyers, Effective C++, Item 36). Class usage is confusing when the behavior depends on the pointer definition instead of the object definition (static binding happening where dynamic binding was expected). This can lead to unsuspected or hard-to-track bugs.
Outside of critical hot spots, correctness usually comes before optimisation, but the current design dates back to main.cpp and it may possibly have been chosen to avoid the overhead of dynamic dispatch. This solution does the same: the class sizes are unchanged and no vptr or vtbl is added.
There are better designs for doing this that use composition instead of inheritance, or that separate the public interface from the private implementations. One example of the latter would be a non-virtual public interface that calls private virtual implementation methods, i.e. the Template pattern via the Non-Virtual Interface (NVI) idiom.
ACKs for top commit:
vasild:
ACK 3a61fc56a0ad6ed58570350dcfd9ed2d10239b48
Tree-SHA512: 9ff358ab0a6d010b8f053ad8303c6d4d061e62d9c3755a56b9c9f5eab855d02f02bee42acc77dfa0cbf4bb5cb775daa72d675e1560610a29bd285c46faa85ab7
fa23c197509f692a815193acc1b50bad2fcbedfe univalue: Avoid narrowing and verbose int constructors (MacroFake)
fa3a9a1e8d9b6dffda772e97c279f3c0af6813f9 rpc: Select int-UniValue constructor for enum value in upgradewallet RPC (MacroFake)
Pull request description:
As UniValue provides several constructors for integral types, the
compiler is unable to select one if the passed type does not exactly
match. This is unintuitive for developers and forces them to write
verbose and brittle code. (Refer to `-Wnarrowing` compiler warning)
For example, there are many places where an unsigned int is cast to a
signed int. While the cast is safe in practice, it is still needlessly
verbose and confusing as the value can never be negative. In fact it
might even be unsafe if the unsigned value is large enough to map to a
negative signed one.
Fix this issue and other (minor) type issues.
ACKs for top commit:
aureleoules:
ACK fa23c197509f692a815193acc1b50bad2fcbedfe.
Tree-SHA512: 7d99b5b90c7d8eed2e3448167255a59e817dd6b8fcfc1b17c69ddefd0db33d1bf4344fbcd8b7f8685b58182c0f572ab9ffa99467afa666ac21843df7ea645033
7ab43eb8110af74e8f5be029118e19b39fe16125 test: remove unused if statements (Aurèle Oulès)
Pull request description:
This change removes two useless if statements in a functional test.
ACKs for top commit:
furszy:
Straightforward ACK 7ab43eb8,
Tree-SHA512: 56ff472f6f53f82d35dead7181dfefa9e7545dfb989e80fb750062a517f0f3c02882db6daa115f2d844f68fac9ce58170c340cf9c9989368419b02fa7f9790e3
9d9a098530df9986039f64b2810b6375b715f196 gui: Fix translator comment for Restore Wallet QInputDialog (w0xlt)
Pull request description:
Fix translator comment for Restore Wallet `QInputDialog`, as suggested in https://github.com/bitcoin-core/gui/pull/471#discussion_r917437779.
This also changes the window title name from `Restore Name` to `Restore Wallet` as it seems clearer.
ACKs for top commit:
shaavan:
reACK 9d9a098530df9986039f64b2810b6375b715f196
Tree-SHA512: 02aec661839215ab1183e4e92fa131671daa986339373a87c0a0e2c5e79a46f362a8846f4a5f6d630a99884a7949031982d13352336bd3f0573625826406dde8
and mark the inherited CBlockIndex#GetBlockHash public interface member
as deleted, to disallow calling it in the derived CDiskBlockIndex class.
Here is a failing test on master demonstrating the inconsistent behavior of the
current design: calling the same inherited public interface functions on the
same CDiskBlockIndex object should yield identical behavior.
```diff
diff --git a/src/test/validation_chainstatemanager_tests.cpp b/src/test/validation_chainstatemanager_tests.cpp
index 6dc522b421..dac3840f32 100644
--- a/src/test/validation_chainstatemanager_tests.cpp
+++ b/src/test/validation_chainstatemanager_tests.cpp
@@ -240,6 +240,15 @@ BOOST_FIXTURE_TEST_CASE(chainstatemanager_activate_snapshot, TestChain100Setup)
const CBlockIndex* tip = chainman.ActiveTip();
BOOST_CHECK_EQUAL(tip->nChainTx, au_data.nChainTx);
+ // CDiskBlockIndex "is a" CBlockIndex, as it publicly inherits from it.
+ // Test that calling the same inherited interface functions on the same
+ // object yields identical behavior.
+ CDiskBlockIndex index{tip};
+ CBlockIndex *pB = &index;
+ CDiskBlockIndex *pD = &index;
+ BOOST_CHECK_EQUAL(pB->GetBlockHash(), pD->GetBlockHash());
+ BOOST_CHECK_EQUAL(pB->ToString(), pD->ToString());
+
```
The GetBlockHash() test assertion only passes on master because the different
methods invoked by the current design happen to return the same result. If one
of the two is changed, it fails like the ToString() assertion does.
Redefining inherited non-virtual functions is well-documented as incorrect
design to avoid inconsistent behavior (see Scott Meyers, "Effective C++", Item
36). Class usage is confusing when the behavior depends on the pointer
definition instead of the object definition (static binding happening where
dynamic binding was expected). This can lead to unsuspected or hard-to-track
bugs.
Outside of critical hot spots, correctness usually comes before optimisation,
but the current design dates back to main.cpp and it may possibly have been
chosen to avoid the overhead of dynamic dispatch. This solution does the same:
the class sizes are unchanged and no vptr or vtbl is added.
There are better designs for doing this that use composition instead of
inheritance or that separate the public interface from the private
implementations. One example of the latter would be a non-virtual public
interface that calls private virtual implementation methods, i.e. the Template
pattern via the Non-Virtual Interface (NVI) idiom.
