nihil.ucl: improve type safety

1 files changed, 81 insertions, 0 deletions

diff --git a/nihil.ucl/object_cast.ccm b/nihil.ucl/object_cast.ccm
new file mode 100644
index 0000000..7291960
--- /dev/null
+++ b/nihil.ucl/object_cast.ccm
@@ -0,0 +1,81 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+module;
+
+#include <cstdlib>
+
+#include <ucl.h>
+
+export module nihil.ucl:object_cast;
+
+import :type;
+import :object;
+import :array;
+
+namespace nihil::ucl {
+
+/*
+ * Ensure a UCL object is convertible to another type.  Throws type_mismatch
+ * if not.
+ */
+
+// Implementation for basic types.
+template<datatype To>
+struct convert_check
+{
+	auto check(::ucl_object_t const *from) -> void
+	{
+		auto from_type = static_cast<object_type>(::ucl_object_type(from));
+		auto to_type = To::ucl_type;
+
+		// Converting from anything to object is permitted.
+		if (to_type == object_type::object)
+			return;
+
+		// Converting between two equal types is permitted.
+		if (from_type == to_type)
+			return;
+
+		// Otherwise, this is an error.
+		throw type_mismatch(to_type, from_type);
+	}
+};
+
+// Implementation for array.
+template<typename T>
+struct convert_check<array<T>>
+{
+	auto check(::ucl_object_t const *from) -> void
+	{
+		using To = array<T>;
+		auto from_type = static_cast<object_type>(::ucl_object_type(from));
+		auto to_type = To::ucl_type;
+
+		// If the source type is not an array, this is an error.
+		if (from_type != object_type::array)
+			throw type_mismatch(to_type, from_type);
+
+		for (std::size_t i = 0, size = ::ucl_array_size(from);
+		     i < size; ++i) {
+			auto const *arr_obj = ::ucl_array_find_index(from, i);
+			convert_check<typename To::value_type>{}.check(arr_obj);
+		}
+	}
+};
+
+/*
+ * Convert a UCL object to another type.
+ */
+export template<datatype To>
+auto object_cast(object const &from) -> To
+{
+	convert_check<To>{}.check(from.get_ucl_object());
+
+	auto const *uobj = from.get_ucl_object();
+	auto *refptr = ::ucl_object_ref(uobj);
+	return To(refptr);
+}
+
+} // namespace nihil::ucl