keel

keel is a lightweight, zero-dependency C++20 foundation library licensed under 0BSD.

It complements the C++ standard library where std is heavy in compile time, Debug runtime overhead, or hidden allocations, while transparently accepting std types at API boundaries via non-owning Ref views.

Design Principles

1. Featherweight Headers: Every public header (include/keel/*.h) is ~100–250 lines and transitively includes only <cstddef>, <cstdint>, and <new> (enforced in CI via /showIncludes and -H).
2. Exception & RTTI Neutral: Compiles cleanly with -fno-exceptions -fno-rtti (/EHs-c- /GR-), while remaining RAII-safe if user callbacks throw.
3. Explicit Ownership & Allocation: Move-only containers with explicit .clone(). Runtime Allocator* pointer stored in containers (no template bloat). First-class virtual-memory Arena and thread-local get_scratch() arenas.
4. Debug Performance: Flat data structures, shallow templates, no base-class chains, compiler builtin traits instead of <type_traits>.
5. UTF-8 Everywhere: All strings and filesystem paths are UTF-8 with / separators; UTF-16 conversion and \\?\ long-path prefixes are hidden inside the Windows platform layer.

Modules

Header	Contents
keel/core.h	i8..u64, f32/f64, isize, usize, KEEL_ASSERT, builtin type traits, move/forward
keel/bits.h	countl_zero, countr_zero, popcount, bit_width, bit_ceil, bit_floor, rotl, rotr, byteswap
keel/hash.h	Fast 64-bit hash_bytes, hash_u64, hash_combine, Hash<T>, Equal<T>
keel/memory.h	Allocator, default_allocator, set_oom_handler, raw memory primitives
keel/arena.h	Virtual-memory Arena (with in-place top realloc), ArenaTemp, thread-local get_scratch
keel/pool.h	Generational slot Pool<T> and 64-bit Handle<T>
keel/ref.h	Non-owning StringRef, ArrayRef<T>, MutArrayRef<T> (accept std ranges without #includes)
keel/error.h	Value-type Error, ErrorCode, ParseError, error_message
keel/result.h	Result<T, E>, KEEL_TRY, KEEL_TRY_ASSIGN
keel/optional.h	Trivially-copyable Optional<T> and zero-size-overhead SentinelOptional<T, Sentinel>
keel/function_ref.h	16-byte non-owning FunctionRef<R(Args...)>
keel/function.h	Move-only inline FixedFunction<R(Args...), N> with zero heap allocations
keel/array.h	Move-only dynamic Array<T> (push_back, remove_at, swap_remove, clone)
keel/small_array.h	FixedArray<T, N> and small-buffer optimized SmallArray<T, N>
keel/ring.h	FixedRing<T, N>, SmallRing<T, N>, and power-of-two circular Ring<T> (Deque<T>)
keel/hash_map.h	Flat open-addressed HashMap<K, V> with 1-byte metadata tags & heterogeneous lookup
keel/hash_set.h	Flat open-addressed HashSet<K>
keel/string.h	FixedString<N>, SmallString<N>, and move-only UTF-8 String (String::from, c_str())
keel/utf8.h	utf8_validate, utf8_decode_next, utf8_encode, utf8_codepoint_count
keel/number.h	Locale-independent integer & shortest round-trip IEEE-754 float/double parsing & formatting
keel/format.h	Type-safe format, format_small, format_fixed, format_into, format_arena, format_buf, print
keel/fs.h	UTF-8 path manipulation (path_join, path_normalize, etc.) and OS filesystem operations
keel/io.h	Move-only File with sticky write errors and console I/O
keel/interop_std.h	Opt-in conversions to std::string, std::string_view, std::vector, std::span, std::optional

Building & Running Tests

cmake -B build
cmake --build build
ctest --test-dir build -C Debug --output-on-failure

License

Zero-Clause BSD (0BSD).