Fixing double bracketing

1 files changed, 21 insertions, 6 deletions

diff --git a/modules/codec/c++/data.hpp b/modules/codec/c++/data.hpp
index c43402e..a8b7836 100644
--- a/modules/codec/c++/data.hpp
+++ b/modules/codec/c++/data.hpp
@@ -330,13 +330,28 @@ public:
 	{
 	}
 
-	/*
+	/**
+	 * Forwarding constructor, so the elements can be written without
+	 * spelling out the inner array.
+	 *
+	 * data<FixedArray<UInt64,3>>{0,1,2} instead of {{0,1,2}}
+	 *
+	 * The guards keep it out of the way of the copy and the meta schema
+	 * constructor in the single element case.
+	 *
+	 * Explicit for a single element, because a one dimensional index would
+	 * otherwise be convertible to both data<UInt64> and this, which makes
+	 * the two at overloads of data<Array<T,1>> ambiguous.
+	 */
 	template<typename... Args>
-	requires (sizeof...(Args) == ct_multiply<uint64_t, D...>::value) &&
-	(std::constructible_from<data<T, encode::Native>, Args> && ...)
-	constexpr data(Args&&... args):
-		value_{ { std::forward<Args>(args)... } } {}
-	*/
+	requires (sizeof...(Args) == ct_multiply<uint64_t, D...>::value)
+		&& (sizeof...(Args) > 1u
+			|| (!std::same_as<std::remove_cvref_t<Args>, data> && ...))
+		&& (!std::same_as<std::remove_cvref_t<Args>, data<MetaSchema, encode::Native>> && ...)
+		&& (std::constructible_from<data<T, encode::Native>, Args> && ...)
+	explicit(sizeof...(Args) == 1u) constexpr data(Args&&... args):
+		value_{ data<T, encode::Native>{std::forward<Args>(args)}... }
+	{}
 
 	SAW_DEFAULT_COPY(data);
 	SAW_DEFAULT_MOVE(data);