Write some notes about file stream.

2 files changed, 31 insertions, 2 deletions

diff --git a/include/cru/common/io/FileStream.h b/include/cru/common/io/FileStream.h
index 6f84526c..333b6d64 100644
--- a/include/cru/common/io/FileStream.h
+++ b/include/cru/common/io/FileStream.h
@@ -1,3 +1,31 @@
+/**
+ * Here are some notes about FileStream:
+ *
+ * 1. FileStream is currently implemented as a typedef of the corresponding
+ * specific XxxFileStream class implemented on each platform and controled with
+ * preprocessor commands. There might be some other ways like proxy pattern but
+ * I do this way for simplicity. So your duty to implement a new platform is to
+ * define a new class and ensure it implements all the required interface. And
+ * in this way you are free to expose any other additional interface like for
+ * specific platform.
+ *
+ * 2. Since each platform defines their own way to open a file, especially the
+ * flags to open a file, we have to define a common interface. I decide to
+ * mimic the C++ std stream open flags
+ * (https://en.cppreference.com/w/cpp/io/basic_filebuf/open) so on platforms
+ * where there is no direct support on certain flags we try our best to
+ * simulate it and make a note for users. The difference between cru design and
+ * std design is:
+ *   1. cru deletes `binary` flag because Stream does not have a so-called
+ * _text_ mode and it is always byte based.
+ *   2. cru adds `OpenFileFlags::Create` and `OpenFileFlags::Exclusive` flags
+ * mimicking Linux behavior which does not exist in std.
+ *
+ * (TODO: Currently the problem is that when I implemented for Windows and UNIX
+ * I didn't take this into consideration so I have to fix this inconsistency
+ * later.)
+ */
+
 #pragma once
 
 #include "../PreConfig.h"
diff --git a/include/cru/common/io/OpenFileFlag.h b/include/cru/common/io/OpenFileFlag.h
index bfbdd38a..bca1d737 100644
--- a/include/cru/common/io/OpenFileFlag.h
+++ b/include/cru/common/io/OpenFileFlag.h
@@ -12,7 +12,8 @@ struct OpenFileFlags {
   static constexpr OpenFileFlag Read{0x1};
   static constexpr OpenFileFlag Write{0x2};
   static constexpr OpenFileFlag Append{0x4};
-  static constexpr OpenFileFlag Create{0x8};
-  static constexpr OpenFileFlag Truncate{0x10};
+  static constexpr OpenFileFlag Truncate{0x8};
+  static constexpr OpenFileFlag Create{0x10};
+  static constexpr OpenFileFlag Exclusive{0x20};
 };
 }  // namespace cru::io