nihil.util/guard.ccm


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// This source code is released into the public domain.
export module nihil.util: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