1 files changed, 105 insertions, 0 deletions
diff --git a/nihil.config/option.ccm b/nihil.config/option.ccm
new file mode 100644
index 0000000..4b95793
--- /dev/null
+++ b/nihil.config/option.ccm
@@ -0,0 +1,105 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+module;
+
+#include <expected>
+#include <iosfwd>
+#include <string>
+
+export module nihil.config:option;
+
+import nihil.error;
+import nihil.ucl;
+
+namespace nihil::config {
+
+/*
+ * Base class for options; this is what config_store interacts with.
+ *
+ * Base classes should override the four protected functions:
+ *
+ * 	get_string()
+ * 	set_string()
+ * 	get_ucl()
+ * 	set_ucl()
+ *
+ * Overriding any other members is not permitted.
+ */
+
+export struct option
+{
+	virtual ~option();
+
+	// Short name of this option.
+	[[nodiscard]] auto name(this option const &) noexcept
+		-> std::string_view;
+
+	// Human-readable description of this option.
+	[[nodiscard]] auto description(this option const &) noexcept
+		-> std::string_view;
+
+	// If true, this option is set to its default value.
+	[[nodiscard]] auto is_default(this option const &) noexcept
+		-> bool;
+
+	/*
+	 * Get or set this option as a string.  The specific conversion
+	 * method depends on the derived option type.
+	 */
+	[[nodiscard]] auto string(this option const &) -> std::string;
+	[[nodiscard]] auto string(this option &, std::string_view value)
+		-> std::expected<void, error>;
+
+	/*
+	 * Return this object as a UCL object.  This is used when writing the
+	 * configuration file.
+	 */
+	[[nodiscard]] auto ucl(this option const &)
+		-> std::expected<ucl::object, error>;
+
+	/*
+	 * Set this object from a UCL object.  This is used when reading the
+	 * configuration file.
+	 */
+	[[nodiscard]] auto ucl(this option &, ucl::object const &)
+		-> std::expected<void, error>;
+
+	// Not copyable or movable.
+	option(option const &) = delete;
+	auto operator=(option const &) -> option& = delete;
+
+protected:
+	option(std::string_view name, std::string_view description);
+
+	auto is_default(this option &, bool) -> void;
+
+	/*
+	 * Get or set this option as a string.
+	 */
+	[[nodiscard]] virtual auto get_string() const
+		-> std::string = 0;
+	[[nodiscard]] virtual auto set_string(std::string_view)
+		-> std::expected<void, error> = 0;
+
+	/*
+	 * Get or set this option as a UCL object.
+	 */
+	[[nodiscard]] virtual auto get_ucl() const
+		-> std::expected<ucl::object, error> = 0;
+	[[nodiscard]] virtual auto set_ucl(ucl::object const &)
+		-> std::expected<void, error> = 0;
+
+private:
+	std::string	m_name;
+	std::string	m_description;
+	bool		m_is_default = true;
+};
+
+/*
+ * Make options printable.  This is mostly useful for testing.
+ */
+export auto operator<<(std::ostream &strm, option const &opt) -> std::ostream &;
+
+} // namespace nihil