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diff --git a/nihil.core/guard.ccm b/nihil.core/guard.ccm
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+// This source code is released into the public domain.
+export module nihil.core:guard;
+
+import nihil.std;
+
+namespace nihil {
+
+// guard: invoke a callable when this object is destroyed; this is similar to
+// scope_exit from the library fundamentals TS, which LLVM doesn't implement.
+export template<std::invocable F>
+struct guard final {
+	// Initialise the guard with a callable we will invoke later.
+	explicit guard(F func) : m_func(std::move(func)) {}
+
+	// We are being destroyed, so call the callable.
+	// If the callable throws, std::terminate() will be called.
+	~guard()
+	{
+		if (m_func)
+			std::invoke(*m_func);
+	}
+
+	// Release the guard.  This turns the destructor into a no-op.
+	auto release(this guard &self) noexcept -> void
+	{
+		self.m_func.reset();
+	}
+
+	// Not default-constructible, movable or copyable.
+	guard() = delete;
+	guard(guard const &) = delete;
+	guard(guard &&) noexcept = delete;
+	auto operator=(this guard &, guard const &) -> guard & = delete;
+	auto operator=(this guard &, guard &&) noexcept -> guard & = delete;
+
+private:
+	// The callable to be invoked when we are destroyed.
+	std::optional<F> m_func;
+};
+
+} // namespace nihil