1 files changed, 200 insertions, 0 deletions
diff --git a/nihil.util/flagset.ccm b/nihil.util/flagset.ccm
new file mode 100644
index 0000000..4c42223
--- /dev/null
+++ b/nihil.util/flagset.ccm
@@ -0,0 +1,200 @@
+// This source code is released into the public domain.
+export module nihil.util:flagset;
+
+/*
+ * flagset: a type-safe flags type.
+ */
+
+import nihil.std;
+
+namespace nihil {
+
+export template <std::integral base_type, typename Tag>
+struct flagset final
+{
+	using underlying_type = base_type;
+
+	/*
+	 * Create an empty flags.
+	 */
+	flagset() noexcept = default;
+
+	/*
+	 * Copyable.
+	 */
+	flagset(flagset const &other) noexcept
+		: m_value(other.m_value)
+	{
+	}
+
+	/*
+	 * Create flags from an integer mask.
+	 */
+	template <base_type flag>
+	[[nodiscard]] static constexpr auto mask() noexcept -> flagset
+	{
+		return flagset(flag);
+	}
+
+	/*
+	 * Create flags for a specific bit.
+	 */
+	template <unsigned bitnr>
+	[[nodiscard]] static constexpr auto bit() noexcept -> flagset
+	{
+		static_assert(bitnr < std::numeric_limits<base_type>::digits);
+		return flagset(static_cast<base_type>(1) << bitnr);
+	}
+
+	/*
+	 * Create flags from a runtime value.
+	 */
+	[[nodiscard]] static auto from_int(base_type value) noexcept -> flagset
+	{
+		return flagset(value);
+	}
+
+	/*
+	 * Assign this flagset.
+	 */
+	auto operator=(this flagset &lhs, flagset rhs) noexcept -> flagset &
+	{
+		if (&lhs != &rhs)
+			lhs.m_value = rhs.m_value;
+		return lhs;
+	}
+
+	/*
+	 * The integer value of this flagset.
+	 */
+	[[nodiscard]] constexpr auto value(this flagset self) noexcept -> base_type
+	{
+		return self.m_value;
+	}
+
+	/*
+	 * True if this flagset has any bits set.
+	 */
+	[[nodiscard]] explicit constexpr operator bool(this flagset self) noexcept
+	{
+		return self.m_value != 0;
+	}
+
+	/*
+	 * Set bits.
+	 */
+	constexpr auto operator|=(this flagset &lhs, flagset rhs) noexcept -> flagset &
+	{
+		lhs.m_value |= rhs.value();
+		return lhs;
+	}
+
+	/*
+	 * Mask bits.
+	 */
+	constexpr auto operator&=(this flagset &lhs, flagset rhs) noexcept -> flagset &
+	{
+		lhs.m_value &= rhs.value();
+		return lhs;
+	}
+
+	/*
+	 * Invert bits.
+	 */
+	[[nodiscard]] constexpr auto operator~(this flagset self) noexcept -> flagset
+	{
+		return flagset(~self.m_value);
+	}
+
+	/*
+	 * xor bits.
+	 */
+	constexpr auto operator^=(this flagset &lhs, flagset rhs) noexcept -> flagset
+	{
+		lhs.m_value ^= rhs.value();
+		return lhs;
+	}
+
+private:
+	base_type m_value = 0;
+
+	explicit constexpr flagset(base_type mask) noexcept
+		: m_value(mask)
+	{
+	}
+
+	[[nodiscard]] friend auto operator|(flagset lhs, flagset rhs) noexcept -> flagset
+	{
+		return (lhs |= rhs);
+	}
+
+	[[nodiscard]] friend auto operator&(flagset lhs, flagset rhs) noexcept -> flagset
+	{
+		return (lhs &= rhs);
+	}
+
+	[[nodiscard]] friend auto operator^(flagset lhs, flagset rhs) noexcept -> flagset
+	{
+		return (lhs ^= rhs);
+	}
+
+	[[nodiscard]] friend auto
+	operator==(flagset lhs, flagset rhs) noexcept -> bool
+	{
+		return lhs.value() == rhs.value();
+	}
+
+	friend auto operator<<(std::ostream &strm, flagset<base_type, Tag> flags) -> std::ostream &
+	{
+		std::print(strm, "{}", flags);
+		return strm;
+	}
+};
+
+} // namespace nihil
+
+/*
+ * Formatting for flagset.
+ */
+export template <std::integral base_type, typename Tag, typename Char>
+struct std::formatter<nihil::flagset<base_type, Tag>, Char>
+{
+	using flags_t = nihil::flagset<base_type, Tag>;
+
+	template <typename ParseContext>
+	constexpr auto parse(ParseContext &ctx) -> ParseContext::iterator
+	{
+		return ctx.begin();
+	}
+
+	template <typename FmtContext>
+	auto format(flags_t flags, FmtContext &ctx) const -> FmtContext::iterator
+	{
+		auto constexpr digits = std::numeric_limits<base_type>::digits;
+		auto value = flags.value();
+		auto it = ctx.out();
+		*it++ = Char{'<'};
+
+		auto printed_any = false;
+
+		for (unsigned i = 0; i < digits; ++i) {
+			unsigned bit = (digits - 1) - i;
+
+			auto this_bit = static_cast<base_type>(1) << bit;
+			if ((value & this_bit) == 0)
+				continue;
+
+			if (printed_any)
+				*it++ = Char{','};
+
+			if (bit > 10)
+				*it++ = Char{'0'} + (bit / 10);
+			*it++ = Char{'0'} + (bit % 10);
+
+			printed_any = true;
+		}
+
+		*it++ = Char{'>'};
+		return it;
+	}
+};