refactor file2 and add span with ownership

solanaceae/file/file2.hpp

@@ -5,6 +5,29 @@
 #include <vector>
 #include <variant>
 
+// TODO: move to/next-to span
+// a span that can also represent its ownership
+template<typename T>
+struct SpanWithOwnership : public Span<T> {
+	// TODO: allow for different owners
+	std::vector<T> _data_owner;
+
+	// self interactions
+	SpanWithOwnership(void) = delete;
+	constexpr SpanWithOwnership(const SpanWithOwnership&) = delete;
+	constexpr SpanWithOwnership(SpanWithOwnership&&) = default;
+
+	// non-owning
+	constexpr SpanWithOwnership(const Span<T>& span) : Span<T>(span) {}
+	constexpr SpanWithOwnership(const Span<T>&& span) : Span<T>(span) {}
+
+	// owning
+	constexpr SpanWithOwnership(std::vector<T>&& data) : Span<T>(data), _data_owner(std::move(data)) {}
+
+	bool isOwning(void) const { return !_data_owner.empty(); }
+};
+using ByteSpanWithOwnership = SpanWithOwnership<uint8_t>;
+
 struct File2I {
 	// read only
 	uint64_t _file_size {0};
@@ -20,6 +43,7 @@ struct File2I {
 
 	// pos -1 means stream, append to last written, or read position (independent, like FILE*s)
 	virtual bool write(const ByteSpan data, int64_t pos = -1) = 0;
-	[[nodiscard]] virtual std::variant<ByteSpan, std::vector<uint8_t>> read(uint64_t size, int64_t pos = -1) = 0;
+	//[[nodiscard]] virtual std::variant<ByteSpan, std::vector<uint8_t>> read(uint64_t size, int64_t pos = -1) = 0;
+	[[nodiscard]] virtual ByteSpanWithOwnership read(uint64_t size, int64_t pos = -1) = 0;
 };