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2678. std::filesystem enum classes overspecified

Section: 31.12.8.2 [fs.enum.file.type], 31.12.8.3 [fs.enum.copy.opts], 31.12.8.6 [fs.enum.dir.opts] Status: C++17 Submitter: Richard Smith Opened: 2016-03-19 Last modified: 2021-06-06

Priority: 3

View all other issues in [fs.enum.file.type].

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Discussion:

The enum class std::filesystem::file_type specifies a collection of enumerators for describing the type of a file, but also specifies (1) the numeric values of the enumerators, and (2) that an implementation cannot extend the list with additional types known to it (and by extension, the standard cannot extend the list in future versions without breakage).

These both seem like mistakes in the design. I would suggest we remove the specification of numerical values, and maybe also

• we allow implementations to add new implementation-defined value

• we replace std::filesystem::file_type::unknown with a value that only means "exists but type could not be determined" and use implementation-specific values for other possibilities.

Similar overspecification exists for std::filesystem::copy_options and std::filesystem::directory_options, where again precise numerical values are specified.

[2016-08 Chicago]

Wed AM: Move to Tentatively Ready

Proposed resolution:

1. Strike the "Value" column from:

   • [fs.enum.file_type], Table 145 Enum class file_type

   • 31.12.8.3 [fs.enum.copy.opts], Table 146 Enum class copy_options

   • 31.12.8.6 [fs.enum.dir.opts], Table 148 Enum class enum.directory_options.

2. Change [fs.enum.file_type] Table 145 Enum class file_type as indicated:

   Constant	Meaning
   none	The type of the file has not been determined or an error occurred while trying to determine the type.
   not_found	Pseudo-type indicating the file was not found. [ Note: The file not being found is not considered an error while determining the type of a file. —end note ]
   regular	Regular file
   directory	Directory file
   symlink	Symbolic link file
   block	Block special file
   character	Character special file
   fifo	FIFO or pipe file
   socket	Socket file
   implementation- defined	Implementations that support file systems having file types in addition to the above file_type types shall supply implementation-defined file_type constants to separately identify each of those additional file types
   unknown	The file does exist, but is of an operating system dependent type not covered by any of the other cases or the process does not have permission to query the file type The file exists but the type could not be determined