MBO, a C++20 library

This C++20 library provides some general useful building blocks and integrates with Google's Abseil library.

The library is tested with Clang (20+) and GCC (13+) on Ubuntu and MacOS (arm) using continuous integration: .

Library organization

The C++ library is organized in functional groups each residing in their own directory:

• Config
  • namespace mbo::config
  • mbo/config:config_cc, mbo/config/config.h
    • Custom Bazel flag --//mbo/config:limited_ordered_max_unroll_capacity which controls the maximum unroll size for LimitedOrdered and thus LimitedMap and LimitedSet.
    • Custom Bazel flag --//mbo/config:require_throws which controls whether MBO_CONFIG_REQUIRE throw exceptions or use crash logging (the default False or 0). This mostly affects containers.
  • mbo/config:require_cc, mbo/config/require.h
    • Marcos MBO_CONFIG_REQUIRE(condition, message) which allows to check a condition and either throw an exception or crash with Abseil FATAL logging. The behavior is controlled by --//mbo/config:require_throws.
• Container
  • namespace mbo::container
  • mbo/container:any_scan_cc, mbo/container/any_scan.h
    • class AnyScan: A container type independent iteration view - or scan over the container.
    • class ConstScan: A container type independent iteration view for const value_types.
    • class ConvertingScan: A container scanner that allows for conversions.
    • function MakeAnyScan: Helper function to create AnyScan instances.
    • function MakeConstScan: Helper function to create ConstScan instances.
    • function MakeConvertingScan: Helper function to create ConvertingScan instances.
  • mbo/container:convert_container_cc, mbo/container/convert_container.h
    • conversion struct ConvertContainer simplifies copying containers to value convertible containers.
  • mbo/container:limited_map_cc, mbo/container/limited_map.h
    • class LimitedMap: A space limited, constexpr compliant map.
  • mbo/container:limited_options_cc, mbo/container/limited_options.h
    • class LimitedOptions: A compile time configuration option for LimitedSet and LimitedMap.
  • mbo/container:limited_set_cc, mbo/container/limited_set.h
    • class LimitedSet: A space limited, constexpr compliant set.
  • mbo/container:limited_vector_cc, mbo/container/limited_vector.h
    • class LimitedVector: A space limited, constexpr compliant vector.
• Diff
  • namespace mbo::diff
  • mbo/diff:diff_cc, mbo/diff/diff.h
    • class Diff: A class that implements line based diffing in unified, context, normal or side-by-side output format (DiffOptions::output_format), using the Myers minimal diff algorithm by default (DiffOptions::algorithm also offers naive and direct).
  • mbo/diff
    • binary diff: A binary that diffs two files; defaults to unified format, --format selects unified, context, normal or side-by-side (--width), --algorithm selects myers (default), naive or direct; --minimal guarantees minimal myers diffs.
  • mbo/diff:diff_bzl, mbo/diff/diff.bzl
    • bzl-macro diff_test: A test rule that compares an output versus a golden file.
• Digest
  • namespace mbo::digest - principles and library docs: mbo/digest/README.md
  • mbo/digest:digest_cc, mbo/digest/digest.h
    • function <algo>::Digest(std::string_view): constexpr-safe, spec-transcribed, vector-pinned message digests; one namespace per algorithm: sha224/sha256/sha384/sha512/sha512_224/sha512_256 (FIPS 180-4), sha3_224/sha3_256/sha3_384/sha3_512 (FIPS 202), blake2b/blake2b_256 (RFC 7693), blake3, and sha1/md5 (legacy interop only; collision-broken).
    • function shake128::Digest<N> / shake256::Digest<N>: the FIPS 202 XOFs - any output length (Algorithm<N> for a fixed size; different lengths share their prefix).
    • function blake3::DigestXof<N> / blake3::DigestKeyed / blake3::DeriveKey<N>: BLAKE3's XOF, keyed, and KDF modes (official-test-vector pinned).
    • function blake2b::Algorithm::DigestKeyed / StreamInitKeyed: BLAKE2b native keying (RFC 7693; keys up to 64 bytes) - BLAKE2 is its own MAC.
    • concept IsDigestAlgorithm / HasStreaming: the algorithm plug-in contract (per-algorithm Algorithm structs).
    • class Streamer<Algo>: incremental digesting (Update(...).Update(...).Finalize(); peekable finalize), guaranteed equal to the one-shot value.
    • struct Hmac<Algo> / class HmacStreamer<Algo>: HMAC (RFC 2104) over any streaming digest (HMAC-SHA3 uses rate-sized blocks per NIST).
    • function ToHexString(digest): lowercase hex, matching hexdigest()/sha256sum presentation.
  • mbo/digest
    • binary digest: checksum-style CLI, byte-compatible with sha256sum/shasum output; -a/--algorithm selects any library algorithm, -c/--check verifies checksum files (coreutils-interchangeable; --quiet, --status, --ignore_missing, --strict), --reverse swaps the columns, -d/--ignore_directories skips directories, - reads stdin.
• Files
  • namespace mbo::files
  • mbo/file:artefact_cc, mbo/file/artefact.h
    • struct Artefact: Holds information about a file (its data content, name, and modified time).
  • mbo/file:file_cc, mbo/file/file.h
    • function GetContents: Reads a file and returns its contents or an absl::Status error.
    • function GetMTime: Returns the last update/modified time of a file or an absl::Status error.
    • function GetMaxLines: Reads at most given number of text lines from a file or returns absl::Status error.
    • function IsAbsolutePath: Returns whether a given path is absolute.
    • function JoinPaths: Join multiple path elements.
    • function JoinPathsRespectAbsolute: Join multiple path elements respecting absolute path elements.
    • function NormalizePath: Normalizes a path.
    • function Readable: Returns whether a file is readable or an absl::Status error.
    • function SetContents: Writes contents to a file.
  • mbo/file:glob_cc, mbo/file/glob.h
    • struct Glob2Re2Options: Control conversion of a glob pattern into a RE2 pattern.
    • struct GlobEntry: Stores data for a single globbed entry (file, dir, etc.).
    • struct GlobOptions: Options for functions Glob2Re2 and Glob2Re2Expression.
    • enum GlobEntryAction: Allows GlobEntryFunc to control further glob progression.
    • type GlobEntryFunc: Callback for acceptable glob entries.
    • function GlobRe2: Performs recursive glob functionality using a RE2 pattern.
    • function Glob: Performs recursive glob functionality using a fnmatch style pattern.
    • function GlobSplit: Splits a pattern into root and pattern parts.
    • program glob: A recursive glob, see glob --help.
  • mbo/file/ini:ini_file_cc, mbo/file/ini/ini_file.h
    • class IniFile: A simple INI file reader.
• Hash
  • namespace mbo::hash - principles and library docs: mbo/hash/README.md
  • mbo/hash:hash_cc, mbo/hash/hash.h
    • function GetHash64<Algo>(std::string_view, seed) / GetHash128<Algo>(std::string_view, seed): A constexpr-safe, non-cryptographic hash; the algorithms default to the in-house mumbo/jumbo family (mumbo for 64-bit, jumbo for the native 128-bit - both SMHasher3-clean, see mbo/hash/README.md) and can be replaced by any IsHashAlgorithm struct. Values are not stable across versions and not for persistence. Big-endian targets are supported by construction (byte-assembled loads) but not exercised by CI.
    • function GetHash32<Algo>(std::string_view, seed): 32-bit companion; uses an algorithm's native 32-bit variant where provided, else the XOR-fold of the 64-bit hash.
    • concept HasGetHash32 / HasGetHash64 / HasGetHash128: Detect which static member functions an algorithm struct provides; IsHashAlgorithm requires a 64- or 128-bit one.
    • struct Hasher<Algo>: Completes any IsHashAlgorithm struct into the full GetHash64/GetHash128/GetHash32 interface, synthesizing what is missing (fold for 64; two decorrelated passes for 128 -- the second skips the first up-to-8 bytes and injects them via the seed). Also a transparent functor over GetHash64, so it drops into absl/std hash containers with heterogeneous string_view lookup.
    • algorithm structs mumbo::Algorithm, jumbo::Algorithm, murmur3::Algorithm, siphash::Algorithm, fnv1a::Algorithm, dumbo::Algorithm (plus rapidhash::Algorithm, xxh3::Algorithm, xxh64::Algorithm via hash_extra.h): the per-algorithm plug-ins for GetHash*<Algo> / Hasher<Algo>.
    • struct Hash128: The 128-bit result type (h1, h2); ordered (<=>) and Abseil hash/stringify compatible.
    • function Hash128To64(Hash128): Folds a 128-bit hash into a well-mixed 64-bit one, e.g. Hash128To64(murmur3::GetHash128(data)).
    • function CombineHashes(uint64_t, uint64_t): Combines two hashes (order-dependent, well mixed).
    • function Hash64To32(uint64_t): Shrinks a hash to 32 bits by XOR-folding the halves (the correct default for all algorithms, incl. weak-low-bit ones like FNV-1a).
    • concept HasStreaming / class Streamer<Algo>: incremental hashing (Update(...).Update(...).Finalize()), guaranteed equal to the one-shot value; provided by mumbo, xxh64, and siphash (rapidhash has no canonical streaming form).
    • function dumbo::GetHash64(std::string_view, seed): the legacy in-house hash (64-bit, weakly seeded, weak mixing; kept for comparison only - use GetHash64 / mumbo instead). Formerly mbo::hash::simple.
    • function fnv1a::GetHash64(std::string_view, seed): canonical FNV-1a 64 (constexpr-safe).
    • function xxh64::GetHash64(std::string_view, seed): canonical XXH64 / xxHash 64-bit (constexpr-safe; in hash_extra.h, see below).
    • function xxh3::GetHash64/GetHash128(std::string_view, seed): canonical XXH3 64- and 128-bit (modern xxHash generation, the fast file-checksum format; scalar; constexpr-safe; in hash_extra.h).
    • function murmur3::GetHash64/GetHash128(std::string_view, seed): canonical MurmurHash3 x64 128-bit (constexpr-safe; GetHash64 is the customary h1 truncation).
    • function rapidhash::GetHash64(std::string_view, seed): canonical rapidhash V3 (wyhash family; SMHasher3-clean; constexpr-safe; in hash_extra.h).
    • function mumbo::GetHash64 / jumbo::GetHash128 (mbo/hash/hash_mumbo.h): the in-house mumbo/jumbo family and default - widening-multiply ("MUM") based, SMHasher3 PASS 188/188 in both widths (the only clean native 128 measured), best mixed-length latency, streaming-capable, notice-free.
    • function siphash::GetHash64(std::string_view, key0, key1) / siphash::SipHash<C, D>(...): canonical SipHash-2-4 (and -1-3 via GetHash64Sip13) - keyed, hash-flooding resistant; adversarial protection requires a secret key.
  • mbo/hash:hash_mangle_cc, mbo/hash/hash_mangle.h
    • function GetHash<Algo, Seed>(std::string_view): as GetHash64 but XORed with one build-selected constant, so values deliberately do not compare across independently configured builds (still constexpr).
    • function HashMangle(uint64_t): XORs the build-selected mangle constant into a hash; identity when built with --//mbo/hash:mangle_seed_buckets=0 (fully reproducible, GetHash == GetHash64).
    • struct MangledHasher<Algo>: Hasher<Algo> extended with the mangled GetHash; the functor form applies the mangle.
    • Custom Bazel flag --//mbo/hash:mangle_seed: any printable-ASCII string (user name, release tag, date) selecting the mangle constant; folded - together with the module version from MODULE.bazel, so every release rotates the constant by construction - to a bucket inside the generation rule, so build caches converge. Only hash_mangle_cc dependents rebuild on rotation.
    • Custom Bazel flag --//mbo/hash:mangle_seed_buckets: bucket count bounding the variation (default 8); 0 disables the mangle (GetHash == GetHash64), 1 pins one stable constant across releases and seeds.
  • mbo/hash:hash_extra_cc, mbo/hash/hash_extra.h
    • The NOTICE-bearing transcriptions (rapidhash MIT; xxh64/xxh3 BSD-2-Clause) as an opt-in target: linking it requires shipping the repository-root NOTICE; the default hash_cc target is notice-free (see "Third-party components").
• Json
  • namespace mbo::json
  • mbo/json:json_cc, mbo/json/json.h
    • class Json: A JSON value/document that can be built from almost any structured type (see ConvertibleToJson) and serialized to JSON text.
    • enum Json::SerializeMode: Selects kCompact, kLine, or kPretty JSON output.
    • function Json::Serialize: Returns the JSON value as a std::string.
    • function Json::Stream: Writes the JSON value to a std::ostream.
    • concept ConvertibleToJson: Determines whether a value can be stored in a Json.
• Log
  • namespace mbo::log
  • mbo/log:demangle_cc, mbo/log/demangle.h
    • functions Demangle to log de-mangled typeid names.
  • mbo/log:log_timing_cc, mbo/log/log_timing.h
    • functoin LogTiming([args]) a simple timing logger.
• Mope
  • namespace mbo::mope
  • The MOPE templating engine. Run bazel run //mbo/mope -- --help for detailed documentation.
  • mbo/mope
    • binary mope.
  • mbo/mope:mope_cc, mbo/mope/mope.h
    • class Template: The mope template engine and data holder.
  • mbo/mope:ini_cc, mbo/mope/ini.h
    • function ReadIniToTemplate: Helper to initialize a mope Template from an INI file.
  • mbo/mope:mope_bzl, mbo/mope/mope.bzl
    • bzl-rule mope: A rule that expands a mope template file.
    • bzl-macro mope_test: A test rule that compares mope template expansion against golden files. This supports clang-format and thus can be used for source-code generation and verification.
• Status
  • namespace mbo::status
  • mbo/status:status_builder_cc, mbo/status/status_builder.h
    • class StatusBuilder which allows to extend the message of an absl::Status.
  • mbo/status:status_cc, mbo/status/status.h
    • function GetStatus allows to convert types to an absl::Status.
  • mbo/status:status_macros_cc, mbo/status/status_macros.h
    • macro MBO_ASSIGN_OR_RETURN: Macro that simplifies handling functions returning absl::StatusOr<T>.
    • macro MBO_MOVE_TO_OR_RETURN: Macro that simplifies handling functions returning absl::StatusOr<T> where the result requires commas, in particular structured bindings.
    • macro MBO_RETURN_IF_ERROR: Macro that simplifies handling functions returning absl::Status or absl::StausOr<T>.
• Strings
  • namespace mbo::strings
  • mbo/strings:indent_cc, mbo/strings/indent.h
    • function DropIndent: Converts a raw-string text block as if it had no indent.
    • function DropIndentAndSplit: Variant of DropIndent that returns the result as lines.
  • mbo/strings:numbers_cc, mbo/strings/numbers.h
    • function BigNumber: Convert integral number to string with thousands separator.
    • function BigNumberLen: Calculate required string length for BigNumer.
  • mbo/strings:parse_cc, mbo/strings/parse.h
    • function ParseString: Parses strings respecting C++ and custom escapes as well as quotes (all configurable).
    • function ParseStringList: Parses and splits strings respecting C++ and custom escapes as well as quotes (all configurable).
  • mbo/strings:split_cc, mbo/strings/split.h
    • struct AtLast: Allows `absl::StrSplit' to split on the last occurrence of a separator.
  • mbo/strings:strip_cc, mbo/strings/strip.h
    • function ConsumePrefix: Removes a prefix from a std::string (like absl::ConsumePrefix).
    • function ConsumeSuffix: Removes a suffix from a std::string (like absl::ConsumeSuffix).
    • function StripPrefix: Removes a prefix from a std::string&& (like absl::StripPrefix).
    • function StripSuffix: Removes a suffix from a std::string&& (like absl::StripSuffix).
    • struct StripCommentsArgs: Arguments for StripComments and StripLineComments.
    • function StripComments: Strips comments from lines.
    • function StripLineComments: Strips comments from a single line.
    • struct StripParsedCommentsArgs: Arguments for StripParsedComments and StripParsedLineComments.
    • function StripParsedComments: Strips comments from parsed lines.
    • function StripLineParsedComments: Strips comments from a single parsed line.
• Testing
  • mbo/testing:matchers_cc, mbo/testing/matchers.h
    • gmock-matcher CapacityIs which checks the capacity of a container.
    • gmock-matcher EqualsText which compares text using line by line unified text diff.
    • gmock-matcher IsElementOf which checks that a value equals at least one element of a container — the element-on-the-left orientation of gmock's Contains. Subject types do not need to be converted to the container's value_type.
    • gmock-matcher IsKeyOf which checks that a value equals at least one key of a map (shorthand for "is this key in the map?").
    • gmock-matcher IsNullopt which compares its argument agains std::nullopt.
    • gmock-matcher IsValueOf which checks that a value equals at least one mapped value of a map (shorthand for "is this value in the map?").
    • gmock-matcher WhenTransformedBy which allows to compare containers after transforming them. This sometimes allows for much more concise comparisons where a golden expectation is already available that only differs in a simple transformation.
    • gmock-matcher-modifier WithDropIndent which modifies EqualsText so that DropIndent will be applied to the expected text.
  • mbo/testing:status_cc, mbo/testing/status.h
    • gmock-matcher IsOk: Tests whether an absl::Status or absl::StatusOr is absl::OkStatus.
    • gmock-matcher IsOkAndHolds: Tests an absl::StatusOr for absl::OkStatus and contents.
    • gmock-matcher StatusIs: Tests an absl::Status or absl::StatusOr against a specific status code and message.
    • gmock-matcher StatusHasPayload: Tests whether an absl::Status or absl::StatusOr payload map has any payload, a specific payload url, or a payload url with specific content.
    • gmock-matcher StatusPayloads Tests whether an absl::Status or absl::StatusOr payload map matches.
    • macro MBO_ASSERT_OK_AND_ASSIGN: Simplifies testing with functions that return absl::StatusOr<T>.
    • macro MBO_ASSERT_OK_AND_MOVE_TO: Simplifies testing with functions that return absl::StatusOr<T> where the result requires commas, in particular structured bindings.
• Types
  • namespace mbo::types
  • mbo/types:cases_cc, mbo/types/cases.h
    • meta-type Cases: Allows to switch types based on conditions.
    • meta-type CaseIndex: Evaluates the first non zero case (1-based, 0 if all zero).
    • meta-type IfThen: Helper type to generate if-then Cases types.
    • meta-type IfElse: Helper type to generate else Cases which are always true and must go last.
    • meta-type IfFalseThenVoid: Helper type that can be used to skip a case.
    • meta-type IfTrueThenVoid: Helper type to inject default cases and to ensure the required type expansion is always possible.
  • mbo/types:compare_cc, mbo/types/compare.h
    • function CompareArithmetic which cmpares two values that are scalar-numbers (including foat/double, excluding pointers and references).
    • function CompareFloat which can compare two float, double or long double values returning std::strong_ordering.
    • function CompareIntegral which compares two values that are integral-numbers (no float/double, no pointers, no references).
    • comparator CompareLess which is compatible to std::Less but allows container optimizations.
    • function CompareScalar which compares two values that are scalar-numbers (including float/double and pointers, excluding references).
    • concept ThreeWayComparableTo which is similar to std::three_way_comparable_with but we only verify that L <=> R can be interpreted as Cat in the presented argument order.
    • function WeakToStrong which converts a std::weak_ordering to a std::strong_ordering.
  • mbo/types:container_proxy_cc, mbo/types/container_proxy.h
    • struct ContainerProxy which allows to add container access to other types including smart pointers of containers.
  • mbo/types:extend_cc, mbo/types/extend.h
    • crtp-struct Extend: Enables extending of struct/class types with basic functionality.
    • crtp-struct ExtendNoDefault Like Extend but without default extender functionality.
    • crtp-struct ExtendNoPrint Like Extend but without Printable and Streamable extender functionality.
    • namespace extender
      • extender-struct AbslStringify: Extender that injects functionality to make an Extended type work with abseil format/print functions. See Stringify for various API extension points.
      • extender-struct AbslHashable: Extender that injects functionality to make an Extended type work with abseil hashing (and also std::hash).
      • extender-struct Comparable: Extender that injects functionality to make an Extended type comparable. All comparators will be injected: <=>, ==, !=, <, <=, >, >=.
      • extender-struct Printable:
        • Extender that injects functionality to make an Extended type get a std::string ToString() const function which can be used to convert a type into a std::string.
        • The output is a comma separated list of field values, e.g. { 25, 42 }.
        • If available (Clang 16+) this function prints field names { .first = 25, .second = 42 }.
      • extender-struct Streamable: Extender that injects functionality to make an Extended type streamable. This allows the type to be used directly with std::ostreams.
  • mbo/types:no_destruct_cc, mbo/types/no_destruct.h
    • struct NoDestruct<T>: Implements a type that allows to use any type as a static constant.
    • Mainly, this prevents calling the destructor and thus prevents termination issues (initialization order fiasco).
  • mbo/types:opaque_cc, mbo/types/opaque.h
    • struct OpaquePtr an opaque alternative to std::unique_ptr which works with forward declared types.
    • struct OpaqueValue an OpaquePtr with direct access, comparison and hashing which will not allow a nullptr.
    • struct OpaqueContainer an OpaqueValue with direct container access.
  • mbo/types:optional_ref_cc, mbo/types/optional_data_or_ref.h
    • concept IsOptionalDataOrRef which determines whether a type is a OptionalDataOrRef.
    • struct OptionalDataOrRef similar to std::optional but can hold std::nullopt, a type T or a reference T&/const T&.
    • struct OptionalDataOrConstRef similar to std::optional but can hold std::nullopt, a type T or a const reference const T&.
  • mbo/types:optional_ref_cc, mbo/types/optional_ref.h
    • concept IsOptionalRef which determines whether a type is a OptionalRef.
    • struct OptionalRef similar to std::optional but can hold std::nullopt or a reference T&/const T&.
  • mbo/types:ref_wrap_cc, mbo/types/ref_wrap.h
    • template-type RefWrap<T>: similar to std::reference_wrapper but supports operators -> and *.
  • mbo/types:required_cc, mbo/types/required.h
    • template-type Required<T>: similar to RefWrap but stores the actual type (and unlike std::optional cannot be reset).
  • mbo/types:stringify_cc, mbo/types/stringify.h
    • class Stringify a utility to convert structs into strings.
    • function StringifyWithFieldNames a format control adapter for Stringify.
    • struct StringifyFieldOptions which controls outer and inner options (both a const StringifyOptions&).
    • struct StringifyOptions which can be used to control Stringify formatting.
    • struct StringifyRootOptions which can be used to control outer/root options for streaming/printing structs.
    • API extension point type MboTypesStringifySupport which enables Stringify support even if not otherwise enabled (disables Abseil stringify support in Stringify).
    • API extension point function MboTypesStringifyConvert(I, T, V) allows to control conversion based on field types via a static call to the owning type, receiving the field index, the object and the field value.
    • API extension point type MboTypesStringifyDisable which disables Stringify support. This allows to prevent complex classes (and more importantly fields of complex types) from being printed/streamed using Stringify
    • API extension point type MboTypesStringifyDoNotPrintFieldNames which if present disables field names in Stringify.
    • API extension point function MboTypesStringifyFieldNames which adds field names to Stringify.
    • API extension point function MboTypesStringifyOptions which adds full format control to Stringify.
    • API extension point functoin MboTypesStringifyValueAccess which allows to replace a struct with a single value in Stringify processing.
  • mbo/types:stringify_ostream_cc, mbo/types/stringify_ostream.h
    • operator std::ostream& operator<<(std::ostream&, const MboTypesStringifySupport auto& v) - conditioanl automatic ostream support for structs using Stringify.
    • function SetStringifyOstreamOutputMode which sets global Stringify stream options by mode.
    • function SetStringifyOstreamOptions which sets global Stringify stream options.
  • mbo/types:traits_cc, mbo/types/traits.h
    • concept ConstructibleFrom implements a variant of std::constructible_from that works around its limitations to deal with array args.
    • concept ConstructibleInto determines whether one type can be constructed from another. Similar to std::convertible_to but with the argument order of std::constructible_from.
    • type alias ContainerConstIteratorValueType returned the value-type of the const_iterator of a container.
    • concept ContainerIsForwardIteratable determines whether a types can be used in forward iteration.
    • concept ContainerHasEmplace determines whether a container has emplace.
    • concept ContainerHasEmplaceBack determines whether a container has emplace_back.
    • concept ContainerHasInsert determines whether a container has insert.
    • concept ContainerHasPushBack determines whether a container has push_back.
    • concept ContainerHasForwardIterator determines whether a container has begin, end and std::forward_iterator compliant iterators.
    • concept ContainerHasInputIterator determines whether a container has begin, end and std::input_iterator compliant iterators.
    • type alias GetDifferenceType is either set to the type's difference_type or std::ptrdiff_t.
    • concept HasDifferenceType determines whether a type has a difference_type.
    • concept IsAggregate determines whether a type is an aggregate.
    • concept IsArithmetic uses std::is_arithmetic_v<T>.
    • concept IsBracesConstructibleV determines whether a type can be constructed from given argument types.
    • concept IsCharArray determines whether a type is a char* or char[] related type.
    • concept IsDecomposable determines whether a type can be used in static-bindings.
    • concept IsEmptyType determines whether a type is empty (calls std::is_empty_v).
    • concept IsFloatingPoint determines whether a type is a floating point type (uses std::floating_point).
    • concept IsInitializerList determines whether a type is `std::initializer
    • concept IsScalar uses std::is_scalar_v<T>.
    • concept IsOptional determines whether a type is a std::optional type.
    • concept IsPair determines whether a type is a std::pair type.
    • concept IsReferenceWrapper determines whether a type is a std::reference_wrapper.
    • concept IsSameAsAnyOf which determines whether a type is the same as one of a list of types. Similar to IsSameAsAnyOfRaw but using exact types. The inversion is available as NotSameAsAnyOf.
    • concept IsSameAsAnyOfRaw which determines whether a type is one of a list of types. Similar to IsSameAsAnyOf but applies std::remove_cvref_t on all types. The inversion is available as NotSameAsAnyOfRaw.
    • concept IsScalar uses std::is_scalar_v<T>.
    • concept IsSet determines whether a type is a std::set type.
    • concept IsSmartPtr determines whether a type is a std::shared_ptr, std::unique_ptr or std::weak_ptr.
      • Can be extended with other smart pointers through IsSmartPtrImpl.
    • concept IsStringKeyedContainer which determines whether a type is a container whose elements are pairs and whose keys are convertible to a std::string_view.
    • concept IsTuple determines whether a type is a std::tuple type.
    • concept IsVector determines whether a type is a std::vector type.
  • mbo/types:template_search_cc, mbo/types/template_search.h:
    • template struct BinarySearch implements templated binary search algorithm.
    • template struct LinearSearch implements templated linear search algorithm.
    • template struct ReverseSearch implements templated reverse linear search algorithm.
    • template struct MaxSearch implements templated linear search for last match algorithm.
  • mbo/types:tstring_cc, mbo/types/tstring.h
    • struct tstring: Implements type tstring a compile time string-literal type.
    • operator operator"" _ts: String literal support for Clang, GCC and derived compilers.
  • mbo/types:tuple_cc, mbo/types/tuple.h
    • template struct TupleCat which concatenates tuple types.
  • mbo/types:typed_view_cc, mbo/types/typed_view.h
    • template struct TypedView a wrapper for STL views that provides type definitions, most importantly value_type. That allows such views to be used with GoogleTest container matchers.
  • mbo/types:variant_cc, mbo/types/variant.h
    • concept IsVariant determines whether a type is a std::variant type.
    • concept IsVariantMemberType determine whether a Type is any of the types in a Variant.
    • struct Overloaded which implements an Overload handler for std::visit(std::variant<...>) and std::variant::visit.

Installation and requirements

This repository requires a C++20 compiler (in case of MacOS XCode 15 is needed). This is done so that newer features like std::source_location can be used.

The project only comes with a Bazel BUILD.bazel file and can be added to other Bazel projects.

The project is formatted with specific clang-format settings which require clang 16+ (in case of MacOs LLVM 16+ can be installed using brew). For simplicity in dev mode the project pulls the appropriate clang tools and can be compiled with those tools using bazel [build|test] --config=clang ....

Lint and format are driven by Trunk. Devs are required to install the CLI locally — curl https://get.trunk.io -fsSL | bash — then run trunk check and trunk fmt before pushing. The repo enables trunk-fmt-pre-commit and trunk-check-pre-push so the hooks run automatically once installed. CI runs trunk check only (no auto-fixing on the GitHub side); failing lint must be fixed locally and re-pushed.

MODULES.bazel

Check Releases for details. All that is needed is a bazel_dep instruction with the correct version.

bazel_dep(name = "helly25_mbo", version = "0.0.0")

The Bazel-Central-Registry installation does not provide the LLVM tools and thus does not come with its own compiler — a restriction in how Bazel handles toolchains under bzlmod. To pull in the bundled toolchain, vendor bazelmod/llvm.MODULE.bazel as described in the release notes. Nonetheless all versions can be compiled with GCC 11+, Clang 17+ on Ubuntu and MacOs as enforced by CI. Other platforms and compilers are likely to work as well. However, Windows lacks some of the necessary tools and the library as well as its build system mostly assume Unix-style file and path names. That unfortunately means that on Windows some code cannot even be built.

Presentations

Practical Production-proven Constexpr API Elements

Presented at C++ On Sea 2024, this presentation covers the theory behind:

• mbo::hash::dumbo::GetHash64 (presented as mbo::hash::simple::GetHash),
• mbo::container::LimitedVector,
• mbo::container::LimitedMap, and
• mbo::container::LimitedSet.

Slides are available at:

Third-party components

The hash and digest libraries contain constexpr transcriptions of third-party algorithms. The transcriptions are original code, but some closely follow their reference implementations; the repository-root NOTICE file reproduces the upstream notices, and the list below tracks exactly which headers and Bazel rules make it apply. The project itself is Apache-2.0 (see LICENSE).

NOTICE entries required for license compliance - for these algorithms the licensed reference implementation effectively is the specification, and the transcription follows its expression:

Header	Bazel rule	Upstream	License
mbo/hash/hash_rapidhash.h	//mbo/hash:hash_extra_cc	rapidhash	MIT
mbo/hash/hash_xxh64.h, mbo/hash/hash_xxh3.h	//mbo/hash:hash_extra_cc	xxHash	BSD-2-Clause

NOTICE entries that are courtesy attribution only - public-domain/CC0 upstreams with no notice obligation, recorded for provenance (and to preempt license-scanner findings of structural similarity):

Header	Bazel rule	Upstream	License
mbo/hash/hash_murmur3.h	//mbo/hash:hash_cc	MurmurHash3	public domain
mbo/hash/hash_siphash.h	//mbo/hash:hash_cc	SipHash	CC0 / public domain
mbo/hash/hash_fnv1a.h	//mbo/hash:hash_cc	FNV-1a	public domain
mbo/digest/digest_blake3.h	//mbo/digest:digest_cc	BLAKE3	CC0-1.0 OR Apache-2.0 (CC0 elected)

Everything else is original helly25 code. In particular, all algorithms implemented from public standards carry no upstream code and need no notices: SHA-1/SHA-2/SHA-3/SHAKE (FIPS 180-4 / FIPS 202), MD5 (RFC 1321), BLAKE2b (RFC 7693), and HMAC (RFC 2104), and the default hash algorithms (the in-house mumbo/jumbo family) are original code. Practical rule: only a distribution that includes code from //mbo/hash:hash_extra_cc - directly or transitively - must retain NOTICE; the default //mbo/hash:hash_cc and //mbo/digest:digest_cc carry no compliance obligation (the digest library's only NOTICE entry is courtesy).