Re: [boost] [filesystem] Major changes before standardization

From: Peter Dimov (pdimov_at_[hidden])
Date: 2004-11-15 07:13:04

Peter Dimov wrote:
> Choosing the wrong native character type causes redundant roundtrip
> conversions, one in Boost.Filesystem, one in the OS.

Let me expand on that a little.

It is _fundamentally wrong_ to assume that all present and future OS APIs 
have a single native character type.

Consider a case where a dual API OS has access to two logical volumes C: and 
D:, where the file system on C: stores the filenames as 16 bit UTF-16, and 
the file system on D: uses narrow characters.

Now the behavior of the calls is as follows:

CreateFileA( "C:/foo.txt" ); // char -> wchar_t OS conversion
CreateFileW( L"C:/foo.txt" ); // no OS conversion
CreateFileA( "D:/foo.txt" ); // no OS conversion
CreateFileW( L"D:/foo.txt" ); // wchar_t -> char OS conversion

Furthermore, consider a typical scenario where the application has its own 
"native" character type, app_char_t. In a design that enforces a single 
"native" character type boost_fs_char_t ("native" is a deceptive term due to 
the above scenario), there are potentially redundant (and not necessarily 
preserving) conversions from app_char_t to boost_fs_char_t and then from 
boost_fs_char_t to the filesystem character type.

In my opinion, the Boost filesystem library should pass the application 
characters _exactly as-is_ to the underlying OS API, whenever possible. It 
should not impose its own "native character" ideas upon the user nor upon 
the OS.