add wip span type and new file2 interface and fstream impl.

testing was very minimal

solanaceae/file/file2_std.hpp

@@ -0,0 +1,50 @@
+#pragma once
+
+#include "./file2.hpp"
+
+#include <fstream>
+
+// std fstream backed files
+
+// write steam file
+// no preallocation required, but seeking is disabled
+struct File2WFile : public File2I {
+	std::fstream _file;
+
+	// dont truncate by default
+	File2WFile(std::string_view file_path, bool trunc = false);
+
+	virtual ~File2WFile(void) {}
+
+	bool isGood(void) override;
+
+	bool write(const ByteSpan data, int64_t pos = -1) override;
+	std::variant<ByteSpan, std::vector<uint8_t>> read(uint64_t size, int64_t pos = -1) override;
+};
+
+// read write, requires an existing file, file size is fixed
+struct File2RWFile : public File2I {
+	std::fstream _file;
+
+	// dont truncate by default
+	// pass -1 for fetching the size from file
+	File2RWFile(std::string_view file_path, uint64_t file_size = -1, bool trunc = false);
+
+	virtual ~File2RWFile(void) {}
+
+	bool isGood(void) override;
+
+	bool write(const ByteSpan data, int64_t pos = -1) override;
+	std::variant<ByteSpan, std::vector<uint8_t>> read(uint64_t size, int64_t pos = -1) override;
+};
+
+// cut down interface (write disabled)
+// TODO: remove
+struct File2RFile : public File2RWFile {
+	File2RFile(std::string_view file_path) : File2RWFile(file_path) {}
+	virtual ~File2RFile(void) {}
+	using File2RWFile::isGood;
+	using File2RWFile::read;
+	bool write(const ByteSpan, int64_t = -1) override { return false; }
+};
+